Terminology Flashcards
Describe $PATH
$PATH is a variable that contains a list of directories that are searched for executable files when a user enters a command.
What does . (dot) represent in the command line?
Don’t confuse with the dot (.) regular expression.
. The current directory. Its value can be requested using the pwd command.
What is an absolute filename?
A filename that is complete and starts with the name of the root directory, including all directories up to the current file or directory.
In Linux what is an access control list (ACL)?
In Linux permissions, a system that makes it possible to grant permissions to more than one user and more than one group. Access control lists also allow administrators to set default permissions for specific directories.
What is anacron?
A service that ensures that vital cron jobs can be executed when the server is down at the moment that the job normally should be executed. Can be considered an extension to cron.
What does AND mean?
A logical construction that can be used in scripts. In an AND construction, the second command is executed only after successful execution of the first command.
What is an application profile?
A collection of packages that may be used to install a specific version of software, according to a specific installation profile.
What is an application stream?
A specific version of a dnf module that can be installed as such.
What is the at utility?
A service that can be used to schedule future jobs for one-time execution.
What is an **attribute **?
A property that can be set to a file or directory and that will be enforced no matter which user with access permission accesses the file.
For instance, a file that has the immutable (i) attribute set cannot be deleted, not even by the root user. However, the root user does have the capability to change the attribute, which would allow the root user to delete the file anyway.
What is an audit log?
The main log file in /var/log/audit/audit.log, which by default contains all messages that are logged by the auditd service.
What is auditd?
A service that runs by default on Red Hat Enterprise Linux and can be configured to log very detailed information about what is happening on RHEL.
Auditing is complementary to system logging and can be used for compliancy reasons. On RHEL, the auditing system takes care of logging SELinux-related messages, which makes it a relatively important system.
What is autofs?
A service that takes care of automatically mounting file systems at the moment that a specific directory is accessed.
This service is very useful to ensure the automatic mounting of home directories for users in a centralized user management system, as can be implemented by the LDAP service.
What is automount?
The process that is started by the autofs service. See autofs for more details.
What is a background process?
A process that is running on a system without actively occupying a console.
Processes can be started in the background by adding a & after the command that starts the process. See also foreground process.
What is a backup?
A copy of important data, which can be restored if at any point in time the original data gets lost.
What is Bash?
The default shell that is used on Red Hat Enterprise Linux.
What is Basic Input/Output System (BIOS)?
The first software that is started when a computer starts on older IBM-compatible computers.
Settings in the BIOS can be changed by using the BIOS setup program.
See also Unified Extensible Firmware Interface (UEFI).
What is binary?
A numbering scheme that is based on bit values that can be on or off.
Binary numbers are 0 and 1. Because binary numbers are difficult to use, decimal, hexadecimal, or octal numbers often are used.
What is a boot loader?
Program that is started as the very first thing while starting a computer and that takes care of loading the operating system kernel and initramfs.
What is BtrFS?
A general-purpose Linux file system that is expected to become the default file system on Red Hat Enterprise Linux in a future release.
What is bzip2?
A compression utility that can be used as an alternative to gzip.
What is cache?
In memory management, the area of memory where recently used files are stored.
Cache is an important mechanism to speed up reads on servers.
What does capability refer to?
A specific task that can be performed on Linux.
User root has access to all capabilities; normal users have access to limited sets of capabilities only.
What is a certificate?
In PKI cryptography, contains the public key of the issuer of the certificate. This public key is signed with the certificate of a certificate authority, which guarantees its reliability.
What is a certificate authority (CA)?
A commonly known organization that can be used to guarantee the reliability of PKI certificates.
The certificate authority provides a certificate that can be used to sign public key certificates. Instead of using commonly known organizations, self-signed certificates can be used for internal purposes as well.
What is chrony?
The service that offers time synchronization services in Red Hat Enterprise Linux.
What is chroot?
An environment where a part of the file system is presented as if it were the root of the file system.
Chroot is used as a security feature that hides part of the operating system that is not required by specific services.
What is CIFS?
**Common Internet File System (CIFS) **
The standardized version of the Microsoft Server Message Block (SMB) protocol, which is used to provide access to shared printers, files, and directories in a way that is compatible with Windows servers and clients.
CIFS has become the de facto standard for file sharing in IT.
What is a conditional loop?
In shell scripting, a set of commands that is executed only if a specific condition has been met.
What is a console?
In Linux, the primary terminal where a user works. It is also a specific device with the name /dev/console.
What is a container?
A ready-to-run application that is started from an image and includes all application dependencies.
What is a container engine?
The code that allows containers to run on top of an operating system.
In SELinux, what is context?
In SELinux, a label that is used to define the security attributes of users, processes, ports, and directories. These contexts are used in the SELinux policy to define security rules.
In SELinux, what is a context type?
In SELinux, a label that identifies the SELinux properties of users, ports, and processes.
What is CRI-o?
prounced CRY-o
The default container engine on RHEL 9.
Pronounced CRY-o.
What is a cron?
A service that takes care of starting services repeatedly at specific times.
What is **deduplication **?
A storage technology that analyzes data to be stored on disk and takes out duplicate patterns to allow for more efficient storage.
What is dependency hell?
Situation where for package installation, other packages are needed, which by themselves could require dependencies as well. The problem of dependency hell has been fixed by the introduction of repository-based systems.
In rsyslog, what is a destination?
In rsyslog, the place where log messages should be sent by the logging system.
Destinations are often files, but can also be input modules, output modules, users, or hosts.
What is a device file?
A file that is created in the /dev directory and that is used to represent and interact with a device.
What is a device mapper?
A service that is used by the Linux kernel to communicate with storage devices.
Device mapper is used by LVM, multipath, and other devices, but not by regular hard disks. Device files that are created by device mapper can be found in the /dev/mapper directory.
What is dmesg?
dmesg is a utility that can be used to read the kernel ring buffer, which contains log messages that were generated by the Linux kernel.
What is dnf?
dnf is the new software manager that replaces the yum utility in RHEL 9.
What is Docker?
A common solution to run containers. Docker was the default container solution in RHEL 8 but is no longer supported and was replaced with CRI-o/podman in RHEL 9.
What is dracut?
dracut is a utility used to generate the initramfs, an essential part of the Linux operating system that contains drivers and other vital files required to start a Linux system.
In RHEL what is enforcing mode?
The SELinux mode where SELinux is fully operational and applies all restrictions that have been configured for a specific system.
What does the term environment mean?
The collection of settings that users or processes are using to do their work.
What is epoch time
In Linux, the number of seconds that have passed since epoch (corresponds to midnight on January 1, 1970). Some utilities write epoch time instead of real clock time.
Epoch time is also know as unix time.
What is escaping?
In a shell environment, using special syntax to ensure that specific characters are not interpreted by the shell.
Escaping may be necessary to show specific characters onscreen or to ensure that regular expression metacharacters are not interpreted by the bash shell first.
What is the exec command used for?
Exec is a system call that replaces the current process with another one; this command does not create a new process, it just replaces the bash with the command to be executed. If the exec command is successful, it does not return to the calling process
See also fork.
In NFS what is export?
In NFS, a directory that is shared on an NFS server to allow access to other servers.
What are the three Ext file system version?
Ext2, Ext3, and Ext4
Up to RHEL 6, Ext4 was the default file system. It is now considered inadequate for modern storage needs, which is why Ext4 in RHEL 7 was replaced by XFS as the default file system.
What is an extended partition?
A solution to create more than four partitions on an MBR disk.
What is an external command?
A command that exists as a file on disk.
In rsyslogd what is facility?
facility in rsyslogd is the source where log information comes from.
A strictly limited number of facilities have been defined in rsyslogd.
What is FHS?
Filesystem Hierarchy Standard (FHS) A standard that defines which Linux directories should be used for which purpose. Read man 7 file-hierarchy for a specification of the FHS.
What is a file descriptor?
A pointer that is used by a Linux process to refer to files that are in use by the process.
What is the default management tool for firewall rules in RHEL?
firewalld is the modern service (replacing iptables) that is used since RHEL 7 to implement firewalling based on the Linux kernel firewalling framework.
What is a foreground process?
A process that is running on a system and occupies the console it is running on.
Linux processes that are started by users can be started in the foreground or in the background. If a process has been started as a foreground process, no other processes can be started in the same terminal until it finishes or is moved to the background.
See also background process.
What does fork mean when refering to processes?
A system call that starts a new process as a child of the current process.
This is the default way commands are executed.
See also exec.
What is fstab?
fstab a configuration file that is used on Linux to mount file systems automatically when the system starts.
What is a hard link?
A name associated with an inode. Inodes are used to store Linux files.
An inode contains the complete administration of the file, including the blocks in which the file is stored. A file that does not have at least one hard link is considered a deleted file. To increase file accessibility, more than one hard link can be created for an inode.
What is hardware time?
The time that is provided by computer hardware, typically the BIOS clock.
What is init?
The first process that is started once the Linux kernel and initramfs have been loaded.
From the init process, all other processes are started. As of RHEL 7, the init process has been replaced by Systemd.
What is initramfs?
The initial RAM file system. Contains drivers and other files that are needed in the first stages of booting a Linux system.
On Red Hat Enterprise Linux, the initramfs is generated during installation and can be manually re-created using the dracut utility.
What is inode?
A structure that contains the complete administration of a file.
Every Linux file has an inode, and the inode contains all properties of the file but not the filename.
In rsyslog, what is an input module?
In rsyslog, an input module allows rsyslog to receive log messages from specific sources.
What is an internal command?
An internal command is a part of the shell and does not exist as a file on disk.
What is iptables used for?
iptables is an older solution to create firewall rules on the Linux operating system. As of RHEL 7, iptables has been replaced by firewalld.
It interfaces with the netfilter Linux kernel firewalling functionality and was the default solution to create software firewalls on earlier versions of RHEL.
What is journalctl?
The command used to manage systemd-journald.
What is journald?
systemd-journald is the part of Systemd that takes care of logging information about events that have been happening.
The introduction of journald ensures that information about all services can be logged, regardless of how the service itself is configured to deal with information that is to be logged.
What is the linux kernel?
kernel is the central component of the operating system.
It manages I/O requests from software and translates them into data processing instructions for the hardware in the computer.
