Commands Flashcards
1
Q
Which command enables one to show all available NFS mounts on ‘server1’?
A
showmount -e server1
The ‘-e’ option specifies that the command show the servers export list.
2
Q
Which command can be used to show all available disk space on mounted devices?
A
df -hT
Just ‘df’ works but the ‘-h’ option formats the output in a human readable form and the ‘-T’ option shows which file system type is used on the different mounts.
3
Q
Which command gives an overview of all mounted devices?
A
mount
4
Q
Which command would list all files/directories (including hidden ones) along with their permissions inside a given directory?
A
ls -al
5
Q
Which command would copy the contents of the ‘/etc’ directory (including other directories) to the ‘/tmp’ directory?
A
cp -R /etc /tmp
The -R option stands for recursive and allows subdirectories to be copied as well.
6
Q
Which command would move the ‘myFile’ file to the
‘/tmp’ directory?
A
mv myFile /tmp
7
Q
Which command would enable one to rename ‘myFile’ to ‘myNewFile’ ?
A
mv myFile myNewFile
8
Q
Which command would create a symbolic link to the ‘/etc/passwd’ file in the current directory?
A
ln -s /etc/passwd .
9
Q
Which command would create a new archive named ‘archive.tar’ in the directory ‘/root’, containing the contents of the entire ‘/etc’ directory?
A
tar -cvf /root/archive.tar /etc
The ‘-v’ option can be omitted as it simply lists the verbose output during execution.
The ‘-f’ option is used to specify the name of the archive file. It can often be omitted.
10
Q
How would one add a single file named ‘singleFile’ to the already existing ‘archive.tar’ file?
A
tar -rvf archive.tar singleFile
The ‘-r’ option appends files to an existing archive.
11
Q
Which command lists the contents of a tar archive ‘archive.tar’ without actually extracting it?
A
tar -tvf archive.tar
12
Q
Which command would extract the contents of the ‘/root/archive.tar’ file and move the contents to the ‘/tmp’ directory?
A
tar -xvf /root/archive.tar -C /tmp
Extracting also works like this for compressed archives as tar will automatically recognize compressed content and then decompress it during extraction.
The ‘-C’ option stands for ‘change directory and tells tar to change the directory to where the command output will be placed.
13
Q
Which command would create a compressed archive ‘archive.tar’ of everything within the ‘/etc’ directory and place that compressed archive in the ‘/home’ directory?
A
tar -czvf /home/archive.tar.gz /etc
tar -cjvf /home/archive.tar.bz2 /etc
tar -cJvf /home/archive.tar.xz /etc
All three of the above options work. The ‘-z’ option compresses with gzip. The ‘-j’ option compresses via bzip2 and the ‘-J’ option compresses via xz.
14
Q
Which command would enable one to set the system time to 4:24 P.M. ?
A
date -s 16:24
Normally, ‘date’ retrieves the current time setting but the ‘-s’ option allows one to set the time.
15
Q
Which command sets the hardware time from the system clock?
A
hwclock –systohc
hwclock -w
16
Q
Which command shows epoch time as human-readable time?
A
date -d ‘@nnnnnnnn’
‘nnnnnnnn’ is the number of seconds since midnight on January 1st, 1970.
The ‘-d’ option specifies that the ‘date’ command will take a string specifying a time rather than just displaying the current time.
17
Q
Which command enables you to use NTP time on your server?
A
timedatectl set-ntp 1
18
Q
Which configuration file contains the list of NTP servers to be used?
A
/etc/chrony.conf
19
Q
Which command displays information about the current time sources that ‘chronyd’ is currently accessing?
A
chronyc sources
20
Q
Which commands would you use to display only line number 5 from the file ‘/etc/passwd’?
A
head -n 5 /etc/passwd | tail -n 1
21
Q
Which command filters out just the first field from the file ‘/etc/passwd’?
A
cut -d : -f 1 /etc/passwd
The ‘-d’ option specifies the delimiter used in the file. The ‘-f’ option specifies which field to retrieve.
22
Q
Which extended regular expression will match all files/subdirectories (including ‘/etc’) within the ‘/etc’ directory?
A
grep -rE ‘/etc(/.*)?’
The ‘.’ matches any single character.
The ‘*’ matches zero to an infinite number of the preceding character.
The ‘?’ matches zero or one of the preceding character.
The ‘-r’ option specifies to search files in the current directory and all subdirectories.
23
Q
Which regular expression will match lines that do not begin with a ‘#’ in the file ‘/etc/services’?
A
grep -v ‘^#’ /etc/services
The ‘-v’ option shows lines that do not match the regular expression.
24
Q
Which grep command enables you to see ‘text’ as well as ‘TEXT’ in a file named ‘/home/user/files’?
A
grep -i ‘text’ /home/user/files
The ‘-i’ option makes the regex case insensitive.
25
Which command enables you to replace all occurrences of the word user with the word users in ~/samplefile?
sed -i 's/user/users/g' ~/samplefile
The '-i' option for sed stands for 'in-place' which specifies that the command should edit the file rather than simply outputting the results.
If the 'g' at the end of the command is omitted, only the first occurrence of 'user' would be replaced.
26
Which command will install the appropriate tools for working with containers in RHEL 9?
sudo dnf install container-tools
27
Which command will list both currently running containers and ones that are now inactive?
podman ps -a
If you want to list the root containers, you must use 'sudo podman ps'
28
Which command would run nginx in a container in the background?
podman run -d nginx
The '-d' option stands for detached mode. This essentially runs it like a background daemon.
29
Which command will run an nginx container in interactive TTY mode, along with the '/bin/sh' command?
podman run -it nginx /bin/sh
The '-i' option stands for interactive while the '-t' option gives access to the container TTY. Adding '/bin/sh' to the end tells the container to run the '/bin/sh' command rather than the default command. '/bin/sh' may be the only shell available as containers are minimal environments.
30
What are the two common ways to exit interactive mode in a container?
1. You could type 'exit' into the terminal. This could stop the whole container depending on the primary container command.
2. You could use 'Ctrl-P, Ctrl-Q' to detach. This approach ensures that in all cases the container continues running in the background in detached mode.
30
How could you reconnect to a shell running within a container named 'mybusybox' ?
podman attach mybusybox
This would re-enter the shell running inside the 'mybusybox' container.
31
Which file specifies the container registries to be used?
'/etc/containers/registries.conf' or the user-specific file '~/.config/containers/registries.conf'
32
Which commands will easily show which container registries are currently being used?
podman info | grep -A 10 registries
'podman info' shows general Podman related system information. One could then pipe the output of that command into grep and search for the lines following the 'registries' string.
33
Which command will allow you to access the 'registry.access.redhat.com' registry?
podman login registry.access.redhat.com
Some container registries require that you authenticate before pulling container images.
34
Which command would search all container registries currently being used for 'mariadb' ?
podman search mariadb
35
Which command allows you to inspect container images before pulling them to your machine?
skopeo
'podman inspect' only works on images that are already pulled.
36
Which command lists the container images that are locally available? (already pulled)
podman images
37
Which command would allow you to see the command that a container image named 'docker.io/library/nginx' will run by default when it is started as a container?
podman inspect docker.io/library/nginx | grep -A 10 Cmd
The 'Cmd' section of the inspect output shows the list of default commands to be executed.
38
Which command prints the kernel release for the system?
uname -r
The '-r' option specifies kernel release information.
39
Suppose you have a container running nginx named 'mynginx' and you want to get its kernel release. Which set of commands would accomplish that?
podman exec mynginx uname -r
'podman exec' executes a command in a running container.
40
How would you run an nginx container named 'mynginx' and make it accessible on host port 8080?
podman run --name mynginx -d -p 8080:80 nginx
The '-p' option allows one to specify port mapping.
The host firewall must also be updated to allow traffic through TCP port 8080.
41
How could you find instructions on how to correctly run a specific container named 'examplecontainer' ?
podman inspect examplecontainer | grep -A 10 usage
The 'usage' section can sometimes include instructions for how to run the container. 'podman logs examplecontainer' could also include log information in case of a container failure.
42
How could you run the 'mysql' container with the 'MYSQL_ROOT_PASSWORD' environment variable set to 'password' ?
podman run -d -e MYSQL_ROOT_PASSWORD=password mysql
The '-e' option allows one to specify an environment variable. Multiple '-e' options can be used in sequence.
43
What two things must be prepared before a host directory can be accessed from within a container?
1. The host directory must be writable for the user account that runs the container.
2. The appropriate SELinux context label must be set to container_file_t.
44
Which commands would first create the directory '/opt/dbfiles' and then allow others to write to that directory?
mkdir /opt/dbfiles; chmod o+w /opt/dbfiles
The 'o+w' part gives write permissions to everyone who isn’t the user owner or the group owner.
45
Which command would run a 'mariadb' container with the 'MYSQL_ROOT_PASSWORD' environment variable set to 'password' and also mount the 'user/dbfiles' directory from the host machine to the '/var/lib/mysql' directory from inside the container?
podman run -d --name mymariadb -v user/dbfiles:/var/lib/mysql:Z -e MYSQL_ROOT_PASSWORD=password mariadb
The '-v' option stands for volume and is used to bind a mount volume into the container. Adding the 'Z' option to the end of the volume mount string is necessary to ensure that the correct SELinux labels are set.
Keep in mind, the user who is running the container must be the owner of the host directory that is being mounted.
46
Which command makes Systemd services enabled for the user 'student' start running at system start rather than user log-in?
loginctl enable-linger student
Linger also ensures that the services will continue running after the user logs out.
47
Suppose you want to create a Systemd unit file that will start a container. Which directory must be created to store this Systemd unit file?
~/.config/systemd/user
48
Suppose you want to create a Systemd unit file that will start a container. Which command should be used to create a Systemd unit file based on a container named 'mydb' ?
podman generate systemd --name mydb --files --new
The '--files' option specifies that a '.service' file should be generated. The '--new' option specifies that a new container should be created when the Systemd unit is started and that it should be deleted when stopped.
This '.service' unit file should be generated inside the ~/.config/systemd/user directory. It should also be performed via an SSH session as the relevant user.
49
Once a Systemd unit file for a container named 'mydb' has been created, what two commands should be performed to ensure that it is detected and starts on reboot?
systemctl --user daemon-reload
systemctl --user enable container-mydb.service
The 'daemon-reload' option ensures that Systemd detects the changes. After a reboot, the 'ps faux' command should show that the 'mydb' container is running successfully.
50
Which command switches to the 'tty4' virtual terminal?
chvt 4
51
Which command would allow one to securely connect to remote host 'server2' as user 'linda' with graphical applications support?
ssh -Y linda@server2
The '-Y' option enables support for graphical applications to be used via SSH.
52
Which file can be edited to create a systemwide configuration that permits 'X forwarding', which is starting graphical applications through an SSH session.
Edit the '/etc/ssh/ssh_config' file to include the following line:
ForwardX11 yes
53
Which command can remotely copy all of the '/etc' directory and its contents from server2 to the '/tmp' directory on the local machine.
scp -r server2:/etc/ /tmp
'scp' copies files between hosts on a network via SSH. The '-r' option recursively copies entire directories.
54
How could one open an SFTP prompt as user 'student' on 'server2' ? Then, how would one upload the '/etc/hosts' file to 'server2' ?
sftp student@server2
put /etc/hosts
In an 'sftp' prompt, 'put' is used to upload files to the remote server. 'get' would be used to download a file to the current directory on the local machine. 'lcd' and 'lpwd' are used to run the 'cd' and 'pwd' commands back on the local machine.
55
What would the procedure be for configuring key-based login as the root user via SSH between server1 and server2?
Run 'ssh-keygen' as the root user and accept the defaults.
Run 'ssh-copy-id server2' as root to copy the public key to server2.
Now, 'ssh server2' should automatically connect to server2 as root without asking for the password. Make sure you are logged in as ‘root’ on ‘server1’ for this process.
56
Which command will display information about a user, including the UID and GIDs for all groups to which the user belongs?
id
57
Which command would give the user 'lisa' access to all sudo privileges?
usermod -aG wheel lisa
All members of the group 'wheel' have full sudo privileges. This command adds lisa to the group wheel. The '-a' option stands for append and '-G' specifies a group.
58
Which file contains configuration details for sudo privileges?
/etc/sudoers
Drop-in configuration files can also be added to the '/etc/sudoers.d' directory.
59
Which command allows you to safely edit the sudo privileges?
visudo
60
Which line should be added to '/etc/sudoers' to allow user 'lisa' to add new users and change their passwords but not for the root account?
lisa ALL=/usr/bin/useradd, /usr/bin/passwd, ! /usr/bin/passwd root
61
How could one extend the lifetime of the token that is given for sudo commands to 4 hours?
Add the following line to '/etc/sudoers'
'Defaults timestamp_timeout=240'
62
What is the best way to use pipes with sudo privileges? How could we use this method for reading the contents of '/etc/passwd' and searching for the root user?
sudo sh -c "cat /etc/passwd | grep root"
This allows everything in quotes to be executed as root.
63
Which file stores passwords for user accounts along with other password details?
/etc/shadow
The second field (delimited by colons) stores the hashed password. If the field begins with an '!' then login for the account is currently disabled.
64
Which command would delete user 'lisa' along with her home directory?
userdel -r lisa
The '-r' option removes the user's home directory.
65
Which command would create a user 'linda' who is a member of the secondary groups 'sales' and 'ops' with 'UID 1201' and add a home directory to the user account as well.
useradd -m -u 1201 -G sales,ops linda
The '-m' option creates the home directory. This overrides the 'CREATE_HOME' line in '/etc/login.defs'
The '-u' option allows for a custom UID to be used. And the '-G' option allows for additional groups to be specified.
66
Which configuration file is used to specify which files/directories are created by default in a user's home directory?
/etc/skel
67
How could you change the default shell of user 'caroline' to prevent login?
usermod caroline -s /sbin/nologin
The '-s' option specifies the login shell for the user account.
68
Using the 'passwd' command, how could one set the password for user 'linda' to a minimal usage period of 30 days and an expiry after 90 days, with a warning generated 3 days before expiry?
passwd -n 30 -w 3 -x 90 linda
The '-n' option specifies the minimum usage period. The '-w' option specifies the number of days before the expiration date that a warning be sent out while '-x' specifies the actual expiration date.
69
Which command would set the user account for 'bob' to expire on December 31st, 2025?
chage -E 2025-12-31 bob
The '-E' option specifies the account expiration date.
70
Which command allows one to interactively set the password properties for the user 'anna' ?
chage anna
This will interactively prompt you for each change to be made.
71
Which command lists current password management settings for user 'anna' ?
chage -l
72
What four files are used when constructing a user environment?
'/etc/profile' is used for default settings for all users when starting a login shell
'/etc/bashrc' is used to define defaults for all users when starting a subshell
'~/.profile' or '~/.bash_profile' specifies settings for one user applied when starting a login shell
'~/.bashrc' specifies settings for one user applied when starting a subshell
These four files are read in the order they are listed upon login.
73
How would one set the default editor to 'vim' for the user 'lisa' ?
Add the following line to '/home/lisa/.bashrc'
'export EDITOR=/usr/bin/vim'
74
Which file holds group information, such as the members for each group?
/etc/group
75
Which command will list the users that are members of group 'sales' ?
lid -g sales
The '-g' option specifies that a group will be the argument. If used without the '-g' option, 'lid' will list groups to which the invoking user belongs.
76
Which command creates new groups?
groupadd
77
Which command will remove the user 'linda' from the group 'students' ?
gpasswd -d linda students
The 'gpasswd' command allows one to administer the '/etc/group' and '/etc/gshadow' files. The '-d' option stands for delete and allows one to specify a user to be removed from a group.
78
Which command will show all files on the machine that have the user 'bob' as their owner?
find / -user bob
This searches everything within the directory '/' for files that are owned by user 'bob'
The 'find' command can also use '-group' to search for files owned by a specific group.
79
Which command will change ownership for the directory '/files' and everything within it to the user 'linda' ?
chown -R linda /files
The '-R' option tells the command to recursively set the permissions for everything within the directory as well as the directory itself.
80
Which command will change the group owner of the directory named '/photos' and its contents to 'artists' ?
chown -R :artists /photos
chgrp -R artists /photos
The syntax for specifying users/groups with chown is:
'chown user:group file'
81
Which command will list the groups a user belongs to?
groups
The first group in the list output is the current primary group for the user.
'sudo lid "username" ' also works.
82
Which command can be used to temporarily change the primary group for the current user to 'sales' ?
newgrp sales
This will open a new shell, in which the new temporary primary group is set to 'sales' until the user logs out or uses the 'exit' command.
83
What are the numeric values of the read, write and execute permissions on Linux?
Read: 4
Write: 2
Execute: 1
84
Which command would allow the owner of the file '/somefile' to read, write and execute, the group owner to read and execute and all others to read and execute?
chmod 755 /somefile
This uses 'chmod' in absolute mode which replaces all current permissions with the ones given as an argument.
85
Which command will give write permissions to the group owner of '/home/somefile' and take away read permissions for all other users?
chmod g+w,o-r /home/somefile
This uses 'chmod' in relative mode when permissions can be added/subtracted from the already existing configuration.
86
Which command would give execute permissions to all three permission groups (users, groups, others) for every subdirectory inside '~/files' in addition to the '~/files' directory itself?
chmod -R a+X ~/files
The 'a' stands for all three permission groups. The '-R' option recursively applies permissions to everything within the directory given. Lastly, the uppercase 'X' only sets execute permissions on the subdirectories rather than both the directories and the files.
87
Suppose there is an executable file named '/usr/bin/action' and it is owned by the root user. Which command can be used to allow any user to run the executable file but only as the owner (root).
chmod u+s /usr/bin/action
's' means both execute and SUID are set while an uppercase 'S' would mean only SUID is set.
88
Suppose there is a shared directory '/accounting' that is owned by the 'accounting' group. Which command would make it so that every file/subdirectory created inside '/accounting' inherits the group ownership?
chmod g+s /accounting
's' means both SGID and execute are set while an uppercase 'S' would mean only SGID is set.
If just SGID is set on a file, then users would execute that file as the group owner.
88
Suppose there is a shared directory '/accounting' that is owned by the 'accounting' group. Which command would make it so that only users who own a file/directory within '/accounting' are allowed to delete them?
chmod +T /accounting
This is known as the sticky bit. This prevents users from deleting files from other users.
89
Which command will list the umask that is set for the current user?
umask
The 'umask' is subtracted from the maximum permissions of 666 for a file and 777 for a directory.
90
What steps would you take to change the default umask to 022 for every user?
1. Create the '/etc/profile.d/umask.sh' file.
2. Add the line 'umask 022' and save the changes.
3. On next login, the umask should be set to 022 for everyone.
A user-specific umask can be defined in the '~/.profile' or '~/.bash_profile' file.
91
Which command would make the memory used for the data in file '/somefile' be written over with 0s after deletion?
chattr +s /somefile
The '+s' attribute overwrites the blocks where the file was stored with 0s after the file has been deleted. This makes sure that recovery of the file is not possible after it has been deleted.
Attributes set via 'chattr' do their work regardless of the user who accesses the file.
92
Which command would make the file '/root/myfile' immutable? This would prevent anyone from editing/deleting it, including the root user.
chattr +i /root/myfile
This attribute can be removed with 'chattr -i'
93
Which command can be used to register a RHEL system?
subscription-manager register
This will prompt for the name of your Red Hat user account as well as your password, and after you enter these, your RHEL server will be registered.
94
Once registered, which command will subscribe the system and give access to updates for Red Hat products?
subscription-manager attach --auto
95
Which directory stores the '.repo' files that are used to configure the server to use specific repositories?
'/etc/yum.repos.d'
96
What five parameters are commonly found in a '.repo' repository client file?
[label]
name=
baseurl=
enabled=
gpgcheck=
97
Suppose the contents of the RHEL 9 installation disk is copied to the '/repo' directory. Which command would automatically create the repository client file for the BaseOS repository?
dnf config-manager --add-repo=file:///repo/BaseOS
Since the repository is installed locally, the 'file://' URI must be used. Ensure that the 'gpgcheck' parameter in the generated repository file is set to 0 to prevent dnf from doing GPG checks on incoming packages.
98
Which command will search through the package names and summaries for a provided keyword?
dnf search "keyword"
dnf search all "keyword"
The 'dnf search all' version of the command also searches through the large package descriptions in addition to the names/summaries.
99
Which command would look for the package containing the file 'Containerfile' ?
dnf whatprovides */Containerfile
dnf provides */Containerfile
dnf wp */Containerfile
All three of these commands provide the same output. The '*' is used because these commands only look for full pathnames.
100
Which command will retrieve information on the 'nmap' package?
dnf info nmap
101
How would one list all packages that are installed on the server?
dnf list installed
102
Which command will update the kernel?
dnf update kernel
Unlike other 'dnf update' commands, updating the kernel will still keep the old version of the kernel around. During the boot process, you can choose which kernel version to use.
103
Which command would show information about the packages available in the group 'Container Management' ?
dnf group info "Container Management"
104
Which command would list all available package groups, including hidden subgroups?
dnf group list hidden
'dnf group list' only shows environment groups and not all subgroups.
105
Which command would allow you to undo the second action performed by dnf?
dnf history undo 2
When using 'dnf history' all dnf commands that were used by the user are listed. 'dnf history undo' then allows users to undo these actions.
106
Which command will show the repositories that the system is currently using?
dnf repolist
107
Which command would show all of the available streams for the 'maven' module?
dnf module list maven
108
Suppose you want to use the 'maven' module with stream 8.1. Which command would show the profiles available for that specific module/stream?
dnf module info maven:8.1
109
Which command would enable the 8.2 stream for the 'maven' module?
dnf module enable maven:8.2
By default, a specific module stream is enabled. This is the module stream that will automatically be used when installing packages. This can be changed with the 'dnf module enable' command.
After switching streams, it is a good idea to execute 'dnf distro-sync' to ensure that all dependent packages that are not in the module itself are updated as well.
110
Which command would find the name of the RPM package that the '/bin/ls' command belongs to?
rpm -qf /bin/ls
The '-q' option stands for query. This option tells the command to query the package database. The '-f' option takes a filename as an argument and will find the specific RPM package a file belongs to.
111
Which command would query the specific RPM file 'httpd- 2.4.6-19.el7.centos.x86_64.rpm' to see whether it contains any scripts before installation?
rpm -qp --scripts httpd- 2.4.6-19.el7.centos.x86_64.rpm
The '-p' option is used to query RPM packages instead of the local RPM package database. The '--scripts' option uses the RPM database to show scripts that are used in the package.
When querying a package, you need to refer to the complete filename, including the version number and all other information. Additionally, the 'rpm' command can only perform this query on RPM packages on the local machine. (either they are already installed or downloaded)
112
Which command can be used to download the 'zsh' package from a repository to the current directory?
dnf download zsh
The 'yumdownloader' command from the 'yum-utils' package used to be used instead.
113
Which command can be used to query packages from the repositories before they have been installed?
repoquery
This command is included in the 'dnf-utils' RPM package.
114
Which command will simply list the current network settings?
ip a
ip a s
ip addr show
All three of the above commands will work. This command will list all network interfaces on the computer, along with some of their configuration details.
115
Which command would temporarily change the link state to UP for the 'eno2' interface?
ip link set dev eno2 up
Every configuration change made with the 'ip' command is non-persistent.
116
Which command will show the link state of all network interfaces along with current link statistics?
ip -s link show
117
Which command will list routing table information?
ip route show
118
Which command can list all TCP ports that are currently listening?
ss -lt
The 'ss' command stands for socket statistics. The '-l' option specifies that only 'Listening' ports should be listed while the '-t' option specifies that only TCP ports should be shown.
Another useful option is the '-n' option which tells the command not to resolve service names but instead show actual numeric port numbers. For example, normally 'ssh' would be listed but the '-n' option would show 22 instead.
119
Which command can show the status of the main network management service?
systemctl status NetworkManager
120
Which command will list all connections?
nmcli con show
121
Which command would create a new connection named 'main-connection' on interface 'ens33' that receives its IPv4 configuration dynamically via DHCP?
nmcli con add con-name main-connection type ethernet ifname ens33 ipv4.method auto
The 'nmcli' connection has great command-line completion to help in composing these longer commands. Just make sure the 'bash-completion' package is installed.
122
Suppose you have a static connection named 'static-connection' and you want to add a second IP address '10.0.0.62/24' to its IPv4 configuration. Which command will accomplish this?
nmcli con mod static-connection +ipv4.addresses 10.0.0.62/24
122
Suppose you have a static connection named 'static-connection' and you wish to add a DNS server with the address '8.8.8.8' to its configuration. Which command will accomplish this?
nmcli con mod static-connection ipv4.dns 8.8.8.8
Notice that while adding a network connection, you use 'ip4', but while modifying parameters for an existing connection, you often use 'ipv4' instead.
122
Suppose you created another network connection named 'main-connection' and you wish to change that to the active connection. Which command will accomplish this?
nmcli con up main-connection
123
Which command will open a text user interface that allows you to create/edit network connections?
nmtui
After editing the connection, you need to deactivate it and activate it again.
124
Which directory stores the '.nmconnection' network configuration files on RHEL 9?
/etc/NetworkManager/system-connections
Older versions of RHEL used the '/etc/sysconfig/network-scripts' directory. If the NetworkManager service finds legacy connection scripts in this directory, they will still be used.
125
Which command will set the host name of the computer to 'myhost.example.com' ?
hostnamectl set-hostname myhost.example.com
You can also edit the '/etc/hostname' file.
Additionally, you can simply execute 'hostnamectl hostname myhost.example.com'
126
Which file stores hostname resolution information?
/etc/hosts
127
Which line could be added to '/etc/hosts' to allow the name 'server5.example.com' to be resolved to the IP address '192.168.20.12' ?
192.168.20.12 server5.example.com
128
Which file stores the information for DNS name server resolution?
/etc/resolv.conf
Do not edit /etc/resolv.conf directly, as it will be overwritten the next time you restart NetworkManager.
129
Which command can verify that host name resolution to 'server2' is working?
getent hosts server2
This command searches in both /etc/hosts and DNS to resolve the host- name that has been specified.
130
Which character can be added to the end of a command to run it in the background?
&
For example: 'sleep 3600 &'
131
Which command will move the last job that was started in the background back as a foreground job?
fg
A specific job ID can be used to bring a specific command back to the foreground.
132
Suppose you have a job running in the foreground that you wish to freeze and then send to the background. Which two steps will accomplish this?
1. 'Ctrl-Z'
2. 'bg'
'Ctrl-Z' will temporarily stop a job so that it can be managed while 'bg' will continue the job that has just been frozen using 'Ctrl-Z' in the background.
133
Which command will list all jobs running from the current shell?
jobs
134
What happens to a background process if its parent process is terminated?
The child process becomes a child of 'systemd'
135
What is an easy way to identify Kernel processes?
When listing all processes, the name of Kernel processes is in between [] brackets.
A system administrator cannot manage Kernel threads.
136
Which command will list all processes along with hierarchical relationships between parent and child processes?
ps fax
137
Which command is the best way to receive a short summary of the active processes?
ps aux
If used without arguments, 'ps' will show only those processes that have been started by the current user.
138
Suppose you run the 'dd if=/dev/zero of=/dev/null &' command as a background process. Which two steps can be taken to lower the priority of this process to 10?
1. ps aux | grep dd
2. renice -n 10 -p 1234 (assuming 1234 is the PID from step 1)
The first step will find the PID for the specific process. The second step will lower the priority of the command. Regular users can only decrease the priority of a running process.
139
Suppose you want to execute the command 'dd if=/dev/zero of=/dev/null &' with a priority of 5. How can you do this?
nice -n 5 dd if=/dev/zero of=/dev/null &
Do not set process priority to –20; it risks blocking other processes from getting served.
140
Which command can show information about running processes in real time?
top
Using 'r' within the 'top' command is another way to renice priority values for processes.
141
Suppose you have a process named 'dd' with a PID of 1370 and you wish to terminate it. How can you do this?
kill 1370
pkill dd
The 'pkill' command takes a process name rather than a PID.
When executed normally, the 'kill' command sends the 'SIGTERM (15)' signal to the process. If you wish to specify the 'SIGKILL (9)' signal, you could've executed 'kill -9 1370'
142
Suppose you have three 'dd' processes running in the background and you wish to terminate all of them simultaneously. How can you accomplish this?
killall dd
143
Suppose you have a zombie process (process that has completed execution but is still listed in the process table) running underneath a parent process with the PID 2072. How can you eliminate this zombie process?
kill -SIGCHLD 2072
This will tell the parent process to remove its child processes. Now the zombie will get adopted by systemd, and after a few seconds it will be removed.
144
How can you find the number of CPU cores in your system?
lscpu
'lscpu' will show various information about the CPU on the machine.
145
Which command will show current load average statistics?
uptime
The load average is shown for the last 1, 5, and 15 minutes. The load average should not be higher than the number of CPU cores in your system.
146
How can you verify that the service that provides a daemon that monitors system activity and provides performance profiles is running?
systemctl status tuned
147
How can you show which 'tuned' profile is currently active?
tuned-adm active
'tuned-adm list' will show the profiles that are available on the server.
148
Suppose you find from the results of the 'tuned-adm recommend' command that the recommended profile for your machine is 'throughput-performance'. How can you change this to be your active profile?
tuned-adm profile throughput-performance
149
Which directory contains default unit files that have been installed from RPM packages.
/usr/lib/systemd/system
You should never edit these files directly.
150
Which directory contains custom unit files?
/etc/systemd/system
151
Which command will list service units on the system?
systemctl -t service
systemctl list-units -t service
Both of the above commands will work. The '-t' option is used to specify the unit file type.
152
Which command will list available Systemd unit types?
systemctl -t help
153
Which command will list both active and inactive service units?
systemctl list-units -t service --all
154
How would you list all units that are required before the 'vsftpd' unit can be started?
systemctl list-dependencies vsftpd --reverse
155
What are some of the common keywords that can be used in unit files to ensure accurate dependency management?
Requires: If this unit loads, units listed here will load also. If one of the other units is deactivated, this unit will also be deactivated.
Requisite: If the unit listed here is not already loaded, this unit will fail.
Wants: This unit wants to load the units that are listed here, but it will not fail if any of the listed units fail.
Before: This unit will start before the unit specified with Before.
After: This unit will start after the unit specified with After.
156
For the current user, how could you make 'vim' the default editor for all commands?
Add the line 'export EDITOR="/usr/bin/vim"' to the files '~/.bashrc' and ' ~/.bash_profile'
'~/.bash_profile' is executed for login shells.
The Systemd default editor can be set specifically by adding 'export SYSTEMD_EDITOR="/usr/bin/ vim"' to the '~/.bashrc' file.
157
Suppose you wish to edit the 'sshd.service' via the 'systemctl edit' command. Which file will be created to contain these new configurations?
/etc/systemd/system/sshd.service.d/override.conf
All settings that are applied in this file overwrite any existing settings in the service file in '/usr/lib/systemd/system'.
158
How could you list all available configuration options for the 'httpd' service unit file?
systemctl show httpd.service
159
Suppose you want the 'httpd' service to always restart if it is terminated. You want this service to automatically restart 5 seconds after termination. How would you accomplish this?
1. Use 'systemctl edit httpd.service' to edit the configuration.
2. Add a '[Service]' section that includes the 'Restart=always' and 'RestartSec=5s' lines.
3. Enter 'systemctl daemon-reload' to ensure that Systemd picks up the new configuration.
160
Which three sections are commonly found in Systemd service unit files?
'[Unit]' Describes the unit and defines dependencies.
'[Service]' Describes how to start and stop the service. Normally includes an 'ExecStop' or 'ExecStart' line.
'[Install]' Indicates in which target this unit has to be started.
161
Suppose you have a Systemd service named 'logrotate.service' and you wish to schedule it to run at specific times. What would be the name of the Systemd unit file responsible for this scheduling?
logrotate.timer
The service unit defines how the service should be started, and the timer defines when it will be started. If you need a service to be started by a timer, you enable the timer, not the service.
162
Timer unit files for Systemd use a [Timer] section to specify the scheduling details. What are some of the common options found in this section?
OnCalendar "Describes when the timer should execute."
AccuracySec "Indicates a time window within which the timer should execute."
Persistent "As a modifier to 'OnCalendar=daily', it would specify that the last execution time should be stored on disk, so that the next time it executes is exactly one day later."
163
When creating new cron jobs, which three locations can be used to store their configurations?
/etc/cron.d
/etc/cron.hourly /etc/cron.daily /etc/cron.weekly
/var/spool/cron
Jobs in '/var/spool/cron' are created via the 'crontab -e' command after logging in as that user or via the 'crontab -e -u "username"' command as root.
The jobs in the 'hourly/daily/weekly/monthly' directories will run automatically due to anacron.
164
Which files can be used to limit which users are allowed to schedule cron jobs?
/etc/cron.allow
/etc/cron.deny
If the cron.allow file exists, a user must be listed in it to be allowed to use cron. If the /etc/cron.deny file exists, a user must not be listed in it to be allowed to set up cron jobs. Both files should not exist on the same system at the same time.
165
How would you schedule a cron job via 'crontab -e' that will execute the following command every weekday at 2 AM:
logger message from root
1. Type 'crontab -e' to open a new file in '/var/spool/cron'
2. Add the line '0 2 * * 1-5 logger message from root'
3. Save the changes and exit the editor
166
How would you schedule a cron job via the 'timed directories' that will, every hour, log a message with the date at time of execution?
1. Create a file with any name in '/etc/cron.hourly'
2. Add the line 'logger Writing log at $(date)'
3. Save the changes and exit the editor
4. Add execute permissions to the file via 'chmod +x'
If you fail to make it executable, it will not work.
167
Which service is used to schedule a non-repeating job to run once at a specific time?
atd
'atd' is the name of the service while the command used to actually schedule a job is 'at'
168
How could you schedule a job that will run only once at 3:00 P.M. and log the message 'this is a single scheduled message' ?
1. Execute 'at 15:00'
2. Type 'logger this is a single scheduled message'
3. Press 'Ctrl-D' to finish scheduling the command
The 'atq' command will list all of the 'atd' jobs that are currently scheduled. 'atrm' can be used to cancel a scheduled 'atd' job.
169
Suppose you want to create a Systemd timer for 'logrotate.service' that will run the service once a day every day. How could you accomplish this?
Create the 'logrotate.timer' file in the '/etc/systemd/system' directory and include the following:
[Unit]
Description=Daily rotation of log files Documentation=man:logrotate(8) man:logrotate.conf(5)
[Timer]
OnCalendar=daily
AccuracySec=1h
Persistent=true
[Install]
WantedBy=timers.target
170
Which directory stores log files that are created by the 'rsyslogd' service?
/var/log
171
Which command would allow you to view logs being added to the '/var/log/messages' file in real time?
tail -f /var/log/messages
172
Which directory stores log messages created by the 'systemd-journald' service?
/run/log/journal
This journal is cleared upon system reboot. To make the journal persistent between system restarts, you should create a directory '/var/log/journal' and set the appropriate ownership settings.
173
Which command lists kernel-related log messages?
dmesg
journalctl --dmesg
174
Suppose you want to show all messages with a priority 'error' that have been written since yesterday. Which command would accomplish this?
journalctl --since yesterday -p err
The '-p' option allows for filtering of messages with a specific priority level.
175
Which file is used to configure settings (such as permanent storage/log rotation) for the 'systemd-journald' service?
/etc/systemd/journald.conf
176
What four possible configurations of the 'Storage' option in '/etc/systemd/journald.conf' are used to determine how the journal is stored after system reboot/shutdown.
Storage=auto "The journal will be written on disk if the directory '/var/log/journal' exists."
Storage=volatile "The journal will be stored only in the '/run/log/journal' directory."
Storage=persistent "The journal will be stored on disk in the directory '/var/log/journal'. This directory will be created automatically if it doesn’t exist."
Storage=none "No data will be stored, but forwarding to other targets such as the kernel log buffer or syslog will still work."
177
What is the process for making the Systemd journal persistent?
1. Open a root shell and type 'mkdir /var/log/journal'
2. Before 'systemd-journald' can write the journal to this directory, you have to set ownership. Type 'chown root:systemd-journal /var/log/journal' followed by 'chmod 2755 /var/log/journal'
3. Use 'systemctl restart systemd-journald' to reload the new 'systemd- journald' parameters.
'systemctl restart systemd-journal-flush' can also be used to ask the journal daemon to flush any log data stored in '/run/log/journal' into '/var/log/journal' if persistent storage is enabled.
178
Which directories/files store the configuration settings for the 'rsyslogd' service?
/etc/rsyslog.conf
/etc/rsyslog.d
179
Suppose you want to create a snap-in file in the '/etc/rsyslog.d' directory to configure 'rsyslog' to log debug messages to the '/var/log/messages-debug' file. How can you do this?
1. Create a file in '/etc/rsyslog.d/' with the '.conf' extension.
2. Add the following line '*.debug /var/log/messages-debug' and save the file.
3. Restart 'rsyslogd' with 'systemctl restart rsyslog'
'rsyslog' rules follow the structure 'facility priority destination'
180
Suppose you want the Apache service to log all errors (only error messages) to the '/var/log/httpd-error.log' file. What steps can be taken to accomplish this?
1. Open the file '/etc/httpd/conf/httpd.conf' in an editor
2. Verify it contains the line 'ErrorLog syslog:local1'
3. Open the file '/etc/rsyslog.conf' in an editor
4. Ensure the file contains the line 'local1.=error -/var/log/httpd-error.log'
5. Execute 'systemctl restart rsyslog'
Using an equals sign in between the facility and priority ensures that only error messages will be logged rather than both errors and every priority above it.
Additionally, including a dash in front of the destination file tells 'rsyslog' to buffer the log messages before immediately committing them to the file for a more efficient write.
181
Which file is used to configure the logrotate service?
/etc/logrotate.conf
The '/etc/logrotate.d' directory can also be used to configure logging for specific services.
182
Which command will list all disk devices available on the system in a hierarchical format?
lsblk
183
Which utilities can be used to create MBR and GPT partitions?
'fdisk' can create both MBR and GPT partitions
'gdisk' can create GPT partitions
184
What are the steps to creating a new 1GiB primary MBR partition on the device '/dev/sdb' ?
1. Execute 'fdisk /dev/sdb'
2. Enter 'n' to create a new partition
3. Press 'p' to choose a primary partition rather than extended
4. For the last sector, type '+1G' to make this a 1-GiB partition
5. Choose the partition type. Linux (83) is the default.
6. Enter 'w' to write the changes to the disk and exit 'fdisk'
185
Suppose your '/dev/sdb' device already has three MBR partitions but you want to have more than four partitions on the device. What are the steps to creating a 1GiB logical partition on this device?
1. Execute 'fdisk /dev/sdb'
2. Type 'n' to create a new partition
3. Enter 'e' to create an extended partition
4. Accept the default sectors for the extended partition (it should fill the rest of the device)
5. Press 'n' to create a logical partition within the extended partition
6. Accept the default first sector
7. For the last sector, enter '+1G'
8. Enter 'w' to write the changes and exit 'fdisk'
An extended partition is used only for the purpose of creating logical partitions. You cannot create file systems directly on an extended partition.
186
What are the steps to creating a new 1 GiB GPT partition on '/dev/sdc' ?
1. Execute 'gdisk /dev/sdc'
2. Type 'n' to create a new partition
3. Enter the number for the partition (usually best to accept default)
4. Specify the size by entering '+1G'
5. Specify the type of the partition (8300 is for a Linux filesystem)
6. Enter 'w' to write the changes and exit 'gdisk'
187
Suppose you have a newly created '/dev/sdc1' partition and you wish to create an XFS filesystem on it. How can you do this?
mkfs.xfs /dev/sdc1
If you use 'mkfs' without any further specification of which file system you want to format, an Ext2 file system will be formatted.
188
Suppose you have an XFS filesystem on '/dev/sdb2'. How would you label that filesystem 'XFSone' ?
xfs_admin -L XFSone /dev/sdb2
The '-L' option is used to specify a label name.
189
Suppose you have an Ext4 filesystem on '/dev/sdc2'. How would you label that filesystem 'ext4one' ?
tune2fs -L ext4one /dev/sdc2
The '-L' option is used to specify a label name.
190
Which command will show (formatted in Mebibytes) how much memory (RAM) and Swap space is being used out of all that is available?
free -m
The '-m' option is used to specify mebibytes.
191
What are the steps to creating/initializing a 1 GiB Swap partition on the '/dev/sdd' device? (assume new partition is '/dev/sdd4')
1. Execute 'fdisk /dev/sdd' (also works with gdisk)
2. Enter 'n' to create a new partition and then specify the size to be '+1G'
3. Enter 't' to change the type to either 82 (fdisk) or 8200 (gdisk)
4. Enter 'w' to write changes and exit
5. Use 'mkswap /dev/sdd4' to format the new partition as swap space
6. Use 'swapon /dev/sdd4' to switch on the newly allocated swap space
7. For the swap space to be mounted automatically, add the following to the '/etc/fstab' file: '/dev/sdd4 none swap defaults 0 0'
192
Which command can be used to list block device information such as UUIDs?
blkid
This command often only works when executed as root.
193
What two commands can be used to verify that changes made to '/etc/fstab' are working?
findmnt --verify
mount -a
'mount -a' will mount all file systems that have a line in '/etc/fstab' and are not currently mounted.
'findmnt --verify' will simply alert you if the syntax in '/etc/fstab' is incorrect.
194
Suppose you want to automatically mount the XFS filesystem on '/dev/vda2' on the '/data' directory. What line should be added to '/etc/fstab' to accomplish this?
/dev/vda2 /data xfs defaults 0 0
195
How could you configure Systemd to automatically mount the Ext4 filesystem '/dev/sdc1' device on to the '/exercise' directory?
Create the '/etc/systemd/system/exercise.mount' file and add the following:
[Unit]
Before=local-fs.target
[Mount]
What=/dev/sdc1
Where=/exercise
Type=ext4
[Install]
WantedBy=multi-user.target
196
What are the three layers when it comes to creating logical volumes?
1. Physical volumes
2. Volume groups
3. Logical volumes
197
Suppose you want to create a physical volume '/dev/sda1' from the '/dev/sda' device. How can you accomplish this?
1. Create a new partition of type 'lvm' via 'fdisk' (8e) or 'gdisk' (8e00) and specify the size
2. Save the changes with 'w'
3. Execute 'pvcreate /dev/sda1' to mark the new partition as an LVM physical volume
198
Which command shows a summary of the physical volumes and their attributes?
pvs
Using 'pvdisplay' on specific partitions can give more detailed information.
199
Suppose you have a physical volume '/dev/sdb3' and you want to create a volume group 'vgdata' and add the physical volume to this volume group. How can you do this?
vgcreate vgdata /dev/sdb3
200
Which command shows a summary of the volume groups on the system?
vgs
Using 'vgdisplay' on specific groups can give more detailed information.
201
Suppose you have a volume group named 'vgdata' and you want to create a logical volume named 'lvdata' in this group. This logical volume should be 5 GiB in size. How can you accomplish this?
lvcreate -n lvdata -L 5G vgdata
The '-n' option is used to specify the name of the LVM logical volume while the '-L' option is used to specify an absolute size.
The '-l' option can be used for relative sizes. For example '-l 50%FREE' would specify that half of the available space on the volume group should be used.
202
Which command shows a summary of all logical volumes?
lvs
203
Suppose you have a volume group named 'vgdata' and you want to add both the '/dev/sdn1' and '/dev/sdv1' physical volumes to the group. How can you do this?
vgextend vgdata /dev/sdn1 /dev/sdv1
204
Suppose you have an LVM logical volume named 'lvdata' in the group 'vgdata' and you want to resize it so that both it and the filesystem residing on it are 20 GiB larger. How can you do this?
lvextend -r -L +20G /dev/vgdata/lvdata
The '-r' option specifies that the filesystem should be resized along with the logical volume.
The '-l' option can also be used to specify relative sizes.
The size of an XFS file system cannot be decreased; it can only be increased. If you need a file system that can be shrunk in size, use Ext4, not XFS.
205
Suppose your volume group 'vgdata' is using two physical volumes, '/dev/sdd3' and '/dev/sdd4'. You want to remove the '/dev/sdd4' physical volume from the volume group. How can you prepare this physical volume so that it can be safely removed?
pvmove /dev/sdd4 /dev/sdd3
This will move all of the extents used on '/dev/sdd4' to '/dev/sdd3'
206
Assuming no extents on '/dev/sdd4' are being used by the 'vgdata' volume group, how can you remove this physical volume from the volume group?
vgreduce vgdata /dev/sdd4
207
What must be done to enable the use of Stratis on a RHEL machine?
1. Install the Stratis software using 'dnf' by installing the 'stratis-cli' and 'stratisd' packages
2. Start and enable the user-space daemon, using 'systemctl enable --now stratisd'
208
Which command would create a new Stratis pool name 'mypool' from the block device '/dev/sde' ?
stratis pool create mypool /dev/sde
209
Suppose you have a Stratis pool named 'mypool' and you wish to add the '/dev/vdb' block device to the pool. Which command would do this?
stratis pool add-data mypool /dev/vdb
210
How can you create a new filesystem named 'myfilesystem' on the Stratis pool 'mypool' ?
stratis fs create mypool myfilesystem
Stratis only supports XFS filesystems.
211
Which command lists all Stratis filesystems?
stratis fs list
212
Suppose you have a Stratis filesystem that you wish to have mounted automatically on the '/data' directory when the system boots. How can you accomplish this?
1. Execute 'stratis fs list' to find the Stratis volume UUID
2. Add the following line to /etc/fstab:
UUID=xxx /data xfs defaults,x-systemd.requires=stratisd.service 0 0
The UUID for the filesystem must be used when mounting Stratis filesystems. Additionally, the mount option 'x-systemd.requires=stratisd.service' must be included to ensure that Systemd waits to activate this device until the stratisd service is loaded.
213
Suppose you have a Stratis filesystem named 'mystratisfs' in a Stratis pool named 'mypool' and you wish to create a snapshot named 'mysnapshot'. Which command would do this?
stratis filesystem snapshot mypool mystratisfs mysnapshot
This snapshot could then manually be mounted (by name) and then accessed.
214
Which directory contains files with status information about the CPU, memory, mounts, and more?
/proc
215
Which file contains information about the RHEL version the machine is using?
/etc/redhat- release
216
What Systemd service is responsible for continuously monitoring plugging and unplugging of new hardware devices?
systemd-udevd
'udevadm monitor' can be executed to monitor events that are processed while activating new hardware devices.
217
Which command lists all kernel modules that are currently being used, along with modules that are using this module?
lsmod
218
Which command would load the vfat kernel module along with its dependencies?
modprobe vfat
'modprobe -r' can be used to unload a module along with its dependencies (if allowed)
219
Which command will upgrade the Linux kernel to the latest version?
dnf upgrade kernel
The kernel files for the last four kernels that you have installed on your server will be kept in the '/boot' directory.
220
What are the four Systemd targets that can be used while booting?
emergency.target
rescue.target
multi-user.target
graphical.target
221
Which command will list all Systemd targets that are currently loaded and active?
systemctl --type=target
222
Which command will list all Systemd targets that exist on the computer?
systemctl -t target --all
223
Suppose you are logged in to a terminal at your server and you need to switch to rescue mode. Which command can do this?
systemctl isolate rescue.target
After finishing in rescue mode, 'systemctl isolate reboot.target' can be used to restart the computer.
224
Suppose you want to set the 'graphical.target' as the default target. Which command will do this?
systemctl set-default graphical.target
'systemctl get-default' will display the current default target
To set the graphical.target as the default target, you need to make sure that the 'server with gui' RPM package group is already installed via 'dnf'
225
Which file can be edited by the administrator to apply changes to the GRUB 2 configuration?
/etc/default/grub
Additionally, the '/etc/grub.d' directory contains complicated shellcode that can be used to further configure GRUB 2.
226
On a BIOS system, where is the main configuration file for GRUB 2 located?
/boot/grub2/grub.cfg
227
On a UEFI system, where is the main configuration file for GRUB 2 located?
/boot/efi/EFI/redhat/grub.cfg
228
In the '/etc/default/grub' file, which boot options should be removed from the 'GRUB_CMDLINE_LINUX' line in order to see messages during boot?
'rhgb' and 'quiet'
With these options enabled, you will not see any messages scrolling by during boot.
229
Which parameter in '/etc/default/grub' is used to configure how long the server will wait for you to access the GRUB 2 boot menu upon system boot?
GRUB_TIMEOUT
For example 'GRUB_TIMEOUT=10' would make the server wait for 10 seconds on the GRUB 2 boot menu before continuing the boot procedure.
230
Suppose you are on a BIOS system and you made some changes to the boot configuration. How can you write these changes to GRUB 2?
grub2-mkconfig -o /boot/grub2/grub.cfg
The '-o' option is used to specify the file where the output should be sent to. On a UEFI machine, this file should be '/boot/efi/EFI/redhat/grub.cfg'
231
Suppose you are in the GRUB 2 boot menu and you wish to configure Linux to boot into emergency mode? What are the steps to accomplishing this?
1. Enter 'e' to configure boot parameters for the kernel you wish to use
2. Find the line that starts with 'linux $(root)/vmlinuz'
3. At the end of this line, add 'systemd.unit=emergency.target'
4. Enter 'Ctrl-X' to to boot
232
What are the steps to restarting a RHEL 9 server from a rescue disk?
1. Restart the server from the installation disk (for a VM, this is configured in VM boot settings)
2. Enter the 'Troubleshooting' menu
3. Select 'Rescue a Red Hat Enterprise Linux System'
4. When prompted about finding an installed Linux system, press '1' to continue
5. Type 'chroot /mnt/sysimage' to ensure that all path references to configuration files are correct
6. When finished, type 'exit' to quit the 'chroot' environment and then enter 'reboot' to restart the server
233
Sometimes the GRUB 2 boot loader can break. Suppose you are already in a rescue disk environment and you have already changed the root directory via the 'chroot /mnt/sysimage' command. How can you reinstall GRUB 2?
For a KVM virtual machine server, execute 'grub2-install /dev/vda'
For a physical server or VMWare/Virtual Box server, execute 'grub2-install /dev/sda'
234
How can you repair the 'initramfs' if it is damaged?
Enter the rescue environment and execute the 'dracut --force' command.
During boot, you will know that you have a problem with the 'initramfs' because you’ll never see the root file system getting mounted on the root directory, nor will you see any Systemd units getting started.
235
Suppose there is a problem with one of the filesystem mounts and the boot procedure ends with the message 'Give root password for maintenance.' What can you do to try and fix this?
1. Enter the root password
2. Type 'mount -o remount,rw /' to make sure the root file system is mounted and writable
3. Analyze the '/etc/fstab' file and fix it
236
Suppose you can't remember the root password for a RHEL 9 machine. What are the steps to resetting it?
1. Enter the GRUB 2 menu and press 'e' on the relevant kernel
2. Find the line that loads the kernel and add 'init=/bin/bash' to the end of it
3. Once the root shell is opened, type 'mount -o remount,rw /' to get read/write access to the root filesystem
4. Create a new root password with the 'passwd' command
5. Execute 'touch /.autorelabel' to create this file in the root directory. This file is necessary for SELinux to correctly set the security labels upon reboot.
6. Type 'exec /usr/lib/systemd/systemd' to replace '/bin/bash' with 'Systemd' as the new PID 1.
'exec' must be used to start Systemd because 'exec' will replace the current process with the new process given, rather than starting the process as a child process to the current process.
237
For a Bash shell script, what would be the shebang?
#!/bin/bash
This tells the subshell how to interpret the commands.
238
Which command will print to the console the exit status of the last command?
echo $?
239
Suppose you have a script named 'helloscript' and it is not executable (was not given execute permissions with 'chmod'). How can you execute this script?
bash helloscript
240
In Bash, which special variable refers to all arguments that were used when starting the script?
$@
The '$@' variable can be iterated over via a for loop in Bash:
for i in $@
do
echo $i
done
241
What statement should be placed at the end of every Bash script?
exit 0
This statement will tell the parent shell that the command executed successfully.
242
Which special variable in Bash is a counter that shows how many arguments were used when starting the script?
$#
243
Suppose you want to write a simple Bash script that will take in one variable as 'NAME' and 'echo' it to the console. If no argument was given during the initial execution of the script, one should be requested inside the script. How can this be done?
#!/bin/bash
if [ -z $1 ]; then
echo enter a name
read NAME
else
NAME=$1
fi
echo you have entered the text $NAME
exit 0
'$1' refers to the first argument given to the command. The line 'if [ -z $1 ];' checks whether $1 is empty; if so, it means that no argument was provided when starting this script. Notice that when you’re writing the test command with the square brackets, it is essential to include one space after the opening bracket and one space before the closing bracket; without these spaces, the command will not work.
244
Suppose you are writing a Bash script and you want to test for the existence of the 'myfile' file. What two main options do you have for performing this test?
test -e myfile
[ -e myfile ]
Both of these syntaxes use the 'test' command.
245
Suppose you are writing a Bash script and you want to execute the line 'echo no argument provided' only if the '$1' variable has no value. How can you do this without using an if/else statement?
[ -z $1 ] && echo no argument provided
'&&' is the logical AND and will execute the second part of the statement only if the first part is true. '||' is a logical OR and will execute the second part of the statement only if the first part is not true.
246
How can you write a Bash script that will simply 'echo' the numbers 100 to 1 in descending order?
#!/bin/bash
for (( COUNTER=100; COUNTER > 0; COUNTER-- )); do
echo $COUNTER
done
exit 0
247
Suppose you want to write a simple Bash script that will 'ping' each IP address in the range 192.168.122.120 - 192.168.122.125 and 'echo' a message when the 'ping' does not reach the host. Also make sure to suppress the standard output of the 'ping' command. How can you do this?
#!/bin/bash
for i in {100..105}; do
ping -c 1 192.168.122.$i >/dev/null || echo ping was not successful
done
exit 0
In the above script, the 'echo' command is only being executed when the 'ping' is not successful.
248
Suppose you want to write a simple Bash script that will take a process name as an argument and continuously check all running processes to see whether your provided process is still running. Redirect unnecessary command output to '/dev/null'. How can you do this?
#!/bin/bash
while ps aux | grep $1 | grep -v grep >/dev/null
do
sleep 5
done
clear
echo your process has stopped
exit 0
The pipe to 'grep -v grep' is used to exclude lines containing the 'grep' command from the result.
249
What are the differences between 'while' and 'until' loops in Bash?
A 'while' loop will continue to execute as long as the condition is true. An 'until' loop lasts until the condition is true (or while a condition is false).
250
How can you write a script that takes in an argument and checks whether the argument given was 'start' 'stop' or 'restart'? It should also have a default case as well.
#!/bin/bash
case $1 in
start)
echo You chose to start.
;;
stop)
echo You chose to stop.
;;
restart)
echo You chose to restart.
;;
*)
echo Invalid input.
;;
esac
exit 0
251
Suppose you have a server named 'server1' and you wish to only allow the users 'lisa' and 'matthew' to connect to it via SSH. How can you do this?
1. Open the file '/etc/ssh/sshd_config' in an editor
2. Add the line 'AllowUsers lisa matthew' and save the changes
This will only allow the users 'matthew' and 'lisa' to connect to this server via SSH. Not even 'root' can remotely connect to this server with this setting (although 'sudo -i' and 'su -' will both still work).
252
How can you configure an SSH server to listen on port 2022 rather than the default port 22?
1. Open the file '/etc/ssh/sshd_config' in an editor
2. Add the line 'Port 2022' and close the editor
3. Execute 'semanage port -a -t ssh_port_t -p tcp 2022' to apply the correct SELinux label to port 2022
4. Open the firewall for TCP port 2022 with the command 'firewall-cmd --add-port=2022/tcp --permanent'
5. Execute 'firewall-cmd --reload' to reload the new firewall configuration to runtime
6. Restart 'sshd' via 'systemctl restart sshd'
253
How can you configure your SSH server to verify that the resolved hostname for the remote host maps back to the same IP address that they are using to connect to the server?
Ensure that the 'UseDNS yes' line is included in '/etc/ssh/sshd_config'
This will make the SSH server first perform a reverse DNS lookup on the IP address to find a hostname. The server will then perform a forward DNS lookup on that hostname to see if it matches the original IP address.
This option being set to 'yes' usually involves a significant performance penalty.
254
How can you allow up to 25 sessions to be simultaneously connected to the SSH server from one IP address?
Ensure that the 'MaxSessions' line in '/etc/ssh/sshd_config' is set to 'MaxSessions 25'
255
Suppose you want the SSH server to send packets to the client 60 seconds after no activity has been detected. It should do this 10 times before killing the connection. How can you accomplish this?
1. On the server, open the '/etc/ssh/sshd_config' file in an editor
2. Find the 'ClientAliveInterval' option and set it to 60
3. Find the 'ClientAliveCountMax' parameter and set it to 10
4. Save the changes and exit the file. Restart the sshd service.
There are also client-side counterparts to these options, named 'ServerAliveInternal' and 'ServerAliveCountMax'
256
Which option in '/etc/ssh/ssh_config' can be set to completely disable password-based authentication via SSH?
PasswordAuthentication no
257
Suppose you use a passphrase when initiating an SSH session. What steps can you take to not have to enter the passphrase for each new connection?
1. Type 'ssh-agent /bin/bash' to start the agent for the current (Bash) shell
2. Type 'ssh-add' to add the passphrase for the current user’s private key (you'll be prompted to enter the passphrase you set during key generation). The key is now cached.
3. Connect to the remote server. Notice that there is no longer a need to enter the passphrase
If you log out or close the shell, the ssh-agent will terminate, and the passphrase will be required again the next time you try to use the private key.
258
Which command will install all relevant packages for running an Apache web server?
dnf group install "Basic Web Server"
259
Suppose you are working with a non-graphical RHEL installation. Which command will install a software that will allow you to work with web content from the command line?
dnf install curl
260
What is the main configuration file for Apache?
/etc/httpd/conf/httpd.conf
261
In the main configuration file for Apache, which parameter specifies the default location where the Apache web server will look for its contents?
DocumentRoot
A common default 'DocumentRoot' for Apache is 'DocumentRoot "/var/www/html"'. Apache will by default look for a file named 'index.html'.
262
How can you start the Apache web service?
systemctl enable --now httpd
263
In the main configuration file for Apache, which parameter defines the default directory where Apache will look for its configuration files?
ServerRoot
By default, the '/etc/httpd' directory is used for this purpose.
264
Which directory can be used for drop-in Apache configuration files?
/etc/httpd/conf.d
265
Although not an RHCSA objective, what are the steps to configuring multiple Apache virtual hosts on one machine? Let's assume the IP address for the Apache server is 192.168.4.210 and let's use the names 'account.example.com' and 'sales.example.com' for the two websites.
1. Add lines to the '/etc/hosts' file that make it possible to resolve the names of the virtual host you are going to create to the IP address of the virtual machine. It should look like this:
192.168.4.210 account.example.com account
192.168.4.210 sales.example.com sales
2. On the Apache server, open a root shell and add the following to the '/etc/httpd/conf/httpd.conf' file:
Require all granted
AllowOverride None
3. On the Apache server, open a root shell and create a configuration file with the name 'account.example.com.conf' in the '/etc/httpd/conf.d' directory. Give this file the following content:
ServerAdmin webmaster@account.example.com
DocumentRoot /www/docs/account.example.com
ServerName account.example.com
ErrorLog logs/account.example.com-error_log
CustomLog logs/account.example.com-access_log common
4. Close the configuration file, and from the root shell type 'mkdir -p /www/docs/account.example.com'
5. Create a file with the name 'index.html' in the account document root.
6. Now back on the root shell, create the '/etc/httpd/conf.d/sales.example.com.conf' and use the same format as the 'account.example.com.conf' file. Then create the '/www/docs/sales.example.com' document root, and create a file
'index.html' in it.
7. For the purpose of this exercise only, switch off SELinux using 'setenforce 0'
8. Restart the Apache web server with 'systemctl restart httpd'
266
Which command can be used to determine whether SELinux is currently in enforcing or permissive mode?
getenforce
The 'sestatus -v' command also works.
267
How can you make RHEL 9 boot with SELinux in disabled mode?
Add 'selinux=0' to the '/etc/default/grub' file (to the line that starts the Linux kernel) and then write those changes with 'grub2-mkconfig -o /boot/grub2/grub.cfg'
268
If you don't want SELinux to be disabled, how can you configure SELinux to start in 'enforcing' or 'permissive' mode by default?
Add the line 'SELINUX=enforcing' or 'SELINUX=permissive' to the '/etc/sysconfig/selinux' file.
In 'permissive' mode, SELinux will not deny any permissions but it will still log to the '/var/log/audit/audit.log' file.
269
How can you list SELinux context labels for all files/directories (including hidden ones) in the '/etc' directory?
ls -aZ
The '-Z' option shows context label settings. Many commands support the '-Z' option, including 'ss' and 'ps'
270
The 'semanage' command does not always come with a RHEL installation. Which command can help you figure out which RPM provides it?
dnf whatprovides */semanage
271
Of what three parts does every SELinux context label consist?
User:Role:Type
272
Suppose you've configured an alternate 'DocumentRoot' named '/website' for the Apache web server. Which commands will set the appropriate SELinux context type to the '/website' directory and then apply the policy settings to the filesystem?
semanage fcontext -a -t httpd_sys_content_t "/website(/.*)?"
restorecon -R -v /website
For the 'semanage fcontext' command, the '-a' option is used to add a context type while the '-t' option specifies that we are changing the context type rather than the user or role. For 'restorecon' the '-R' option is used to relabel files/directories recursively while the '-v' option specifies that the command should output the changes that are made.
273
The best way to find the appropriate SELinux context type for a service is via the man pages. Which command will install the RPM package that contains SELinux related man pages?
dnf install selinux-policy-doc
Make sure to execute 'mandb' to update the man pages with the new SELinux content.
274
Suppose you need to set the appropriate SELinux context type for a new Apache document root but you don't remember what context type is required for this scenario. How can you figure out which context type is required.
Execute 'man -k _selinux | grep http' to find the man pages that document SELinux settings for Apache.
You can also examine the default environment for clues. For example, you can use 'ls -Z /var/www' to look at the context type used for the default document root.
275
What are the two methods for relabeling SELinux context labels for the entire filesystem?
1. Execute 'restorecon -Rv /'
2. Create the '/.autorelabel' file and then reboot the system.
276
Suppose you have configured Apache by editing '/etc/httpd/conf/httpd.conf' to listen on port 82 rather than the default port 80. How can you appropriately update the SELinux context label for port 82?
semanage port -a -t http_port_t -p tcp 82
The '-p' option is used to specify the port when using the 'semanage port' command.
277
Which command will list all SELinux booleans on a system?
getsebool -a
'grep' can be used here to filter for specific services such as 'http' or 'ftp'
278
Suppose you want anonymous writes to be configured for your FTP server. How can you configure this via SELinux booleans?
setsebool -P ftpd_anon_write on
The '-P' option specifies that the changes should be permanent rather than only applied to the runtime. 'ftpd_anon_write' is the specific Boolean that enables/disables anonymous writes for the FTP server.
279
What file stores SELinux logs?
/var/log/audit/audit.log
280
Which command will retrieve only SELinux logs from '/var/log/audit/audit.log' ?
grep AVC /var/log/audit/audit.log
SELinux messages are logged with 'type=AVC' in the audit log.
281
The 'sealert' command is used to provide more simplified SELinux log messages. How can this command be installed?
dnf install setroubleshoot-server
Make sure to reboot the server after installing 'sealert' to ensure that all processes that are involved are restarted correctly.
Now, the next time an SELinux message is written to the audit log, an easier-to-understand message is written to the systemd journal.
282
How can you read the 'sealert' messages that are written to the systemd journal?
journalctl | grep sealert
Running the command suggested by 'sealert' will query the SELinux event database and often give suggestions on how to fix the problem.
283
Which directories store XML files that define Firewalld services?
/usr/lib/firewalld/services
The '/etc/ firewalld/services' directory stores custom service XML files.
284
Which command will show all Firewalld services available on the system?
firewall-cmd --get-services
When working with Firewalld, the right services need to be added to the right zones. Also, the firewall configuration can be enhanced with more specific settings if the zones are not robust enough.
285
Which command will show the current default zone being used by the firewall?
firewall-cmd --get-default-zone
If an incoming packet does not belong to a specific zone, the packet is handled by the settings in the default zone.
'firewall-cmd --get-zones' will list all zones available to Firewalld.
286
Which command will show which services are in the current zone?
firewall-cmd --list-services
287
Which command will show an overview of the current firewall configuration?
firewall-cmd --list-all
288
Like many things on RHEL, the Firewalld service has both a runtime firewall configuration and a permanent/on-disk configuration. Which command will reload the on-disk configuration into the runtime configuration?
firewall-cmd --reload
The 'firewall-cmd --runtime-to-permanent' command can be used to make the current runtime configuration the permanent configuration.
289
Which command would add the 'vnc-server' service to the permanent firewall configuration?
firewall-cmd --add-service=vnc-server --permanent
290
Suppose you want your server to allow traffic through TCP port 2020. Which command will add this rule to the permanent firewall configuration?
firewall-cmd --add-port=2020/tcp --permanent
291
On an NFS server, which file defines NFS shares?
/etc/exports
292
Suppose there is an NFS server named 'datashare' that you wish to use. Which command can be used to find out which NFS shares are available?
showmount -e datashare
The 'showmount' command may not work if the the 'mountd' and 'rpc-bind' services are not added to the NFS server firewall configuration.
293
What command will install the packages necessary to enable an NFS server?
dnf install nfs-utils
Make sure to also enable the NFS service with 'systemctl enable --now nfs-server'
294
Suppose you are configuring an NFS server and you want to create an NFS share for the '/nfsdata' directory. What line can you add to the '/etc/exports' file to export this folder?
/nfsdata *(rw,no_root_squash)
In this line, the '*' is used to specify that this export is available to all hosts. The 'rw' option gives read-write access to every remote host. Lastly, the 'no_root_squash' option allows root users to retain their root-level privileges on the NFS server.
Without the 'no_root_squash' option, if a remote user connects as the root user (uid 0), their access is mapped to the 'nfsnobody' user (usually with uid 65534) on the server.
295
Which three services must be added to the permanent firewall configuration on an NFS server? Give the three separate commands.
firewall-cmd --add-service nfs --permanent
firewall-cmd --add-service rpc-bind --permanent
firewall-cmd --add-service mountd --permanent
Do not forget to reload the firewall with 'firewall-cmd --reload'
296
Suppose you are on 'Desktop1' and you wish to mount an NFS share from 'server2' on to your local '/mnt' directory. How can you accomplish this via a root mount?
mount server2.example.com:/ /mnt
In a root mount, you just mount the root directory of the NFS server, and under your local mount point you’ll only see the shares to which you have access.
297
How could you configure the '/nfsdata' directory from the NFS server 'server1' to automatically be mounted on the local '/datashare' directory?
Add the following line to the '/etc/fstab' file:
server1:/nfsdata /datashare nfs sync 0 0
The third column contains the NFS file system type. The 'sync' option ensures that modified files are committed to the remote file system immediately and are not placed in write buffers first (which would increase the risk of data getting lost).
298
In order to work with 'autofs' and Automount, which command will install the tools necessary to configure these services?
dnf install autofs
299
How could you configure the '/nfsdata' directory from 'server2' to automatically mount on the '/nfsdata/files' directory on 'server1' via Automount?
1. Ensure the 'autofs' RPM package is installed on 'server1'
2. Ensure the '/nfsdata' directory is currently being exported on 'server2'
3. Type 'vim /etc/auto.master'
4. Add the line '/nfsdata /etc/auto.nfsdata' and exit the editor
5. Type 'vim /etc/auto.nfsdata'
6. Add the line 'files -rw server2:/nfsdata' and close the editor
7. Run 'systemctl enable --now autofs'
300
Suppose you want to configure wildcard mounts on 'server1' so that when a user accesses their home directory, it is automatically mounted from the '/users' directory on 'server2' onto the corresponding '/home' directory. How can you do this?
1. Add this line to '/etc/auto.master':
/home /etc/auto.users
2. Then, add this line to '/etc/auto.users':
* -rw server2:/users/&
3. Restart the 'autofs' service with 'systemctl restart autofs'
301
Suppose you want to change the Apache configuration via the 'httpd.service' file. Which command will allow you to safely edit this configuration?
systemctl edit httpd.service
This will automatically create the '/etc/systemd/system/httpd.service.d/override.conf' file.
302
What file that holds installation settings/parameters can be automatically created during system installation? This can then be used to install RHEL on other systems with identical settings.
/root/anaconda-ks.cfg
This is a Kickstart file.
303
How can you check whether the CPU is capable of virtualization?
grep -E "svm|vmx" /proc/cpuinfo
'vmx' is the virtualization extension used on Intel CPUs while 'svm' is the the extension used on AMD CPUs.
304
How can you install the group of packages that allows your RHEL machine to be a virtualization host?
dnf group install "Virtualization Host"
305
Which command can check if the prospective virtualization host meets all required conditions?
virt-host-validate
306
Suppose you want to install a virtual machine on your host via the Cockpit web console. Which URL can you use to access the Cockpit console in a web browser?
https://localhost:9090
307
How can you configure Cockpit so that you can use it in the web console/browser?
1. Execute 'dnf install cockpit-machines'
2. Execute 'systemctl enable --now cockpit.socket'
308
Which command will install the package that enables you to install a virtual machine on your RHEL 9 host?
dnf install virt-install
309
How can you install a virtual machine on your RHEL 9 host with the following configuration?
Name: testvm
RAM: 2048 Megabytes
CPU: 2 CPUs
Disk Size: 20 Gigabytes
OS: Linux
Installation Source: /rhel9.iso
virt-install --name testvm --memory 2048 --vcpus 2 --disk size 20 --os-type linux --cdrom /rhel9.iso
310
Suppose you are creating a Kickstart file and you want the installer to prompt for the root password during installation. How can you make this happen?
Simply omit the line that sets the root password from the Kickstart file.
