Working with files and permissions

Question 1

Make dir with subdirs

Answer 1

mkdir -p dir/dir2

Question 2

Copy file with confirmation that a target file already exists

Answer 2

cp -i file1 file1.bak

asks if file1.bak should be overritten

Question 3

Determine file type

Answer 3

file file1.txt=> ASCII text

Question 4

Grep which searches based on strings which might be located in file

Answer 4

fgrep
or grep -F
so, fgrep pattern_file passwd

Question 5

Links

Answer 5

ln -s /etc/passwd my_link
editing symbolic link updates original file as well
if original the file is moved, link will be broken

ln /etc/passwd my_hard_link
____
unlink my_link

Question 6

Finding files

Answer 6

find / -name "*.tar" -ctime 1
use weak quotes when using file globbing
\_\_\_\_\_
-name -name
-ctime -last change time (in days)
-atime -access time (in days)
-empty
-type f or -type -d

find . -name myfile{1..100} -exec rm -rf {} \;

find /text -empty | xargs rm -f

grep -l “junk” test/file_* | xargs -I {} mv {} ~/test/bak

Question 7

stdin, stdout,stderr

Answer 7

stdin: 0
stdout: 1
stderr: 2
shell. sh 2>&1 | less (errors and stdout goes to less)

Question 8

1. Search through local db for files and dirs to match search criteria
2. Update local db

Answer 8

1. locate passwd => a lot of output
   for binaries better use whereis
2. updatedb

locate updatedb.conf

Question 9

Locate binaries, source and man pages

Answer 9

whereis

whereis passwd

Question 10

Read from stdin and write to stdout and file

Answer 10

tee

ls -d ~/doc/lib[Xx]* | tee ./libdocs/

Question 11

grep options

Answer 11

-l -output only file names
-r -recursively
grep -i histfiles* -lr /*
-v -exclude
-i -ignore case

Question 12

Copy and convert files

Answer 12

dd if=boot.img of=/dev/sdc
dd if=/dev/xvda of=/tmp/mbr.img bs=512 count=1
dd if=/dev/urandom of=r_file bs=1024k count=10

Question 13

tar

Answer 13

tar -czf backup.tar.gz ~/mydir
tar -cvjf backup.tar.bz2 ~/mydir
\_\_\_
tar -xzf backup.tar.gz
tar -xvjf backup.tar.bz2

Question 14

Show contents of tar archive

Answer 14

tar -tf mybackup.tar

Question 15

gzip
bzip2
xz

Answer 15

gzip original_file
bzip2 or_file
xz myfile
ls=>original_file.gz, or_file.bz2,myfile.xz

so archiving will remove original ones and add to archive
\_\_\_
gunzip original_file.gz
bunzip2 or_file.bz2
unxz myfile.xz

Question 16

Change file permissions

Answer 16

chmod

chmod -R (recursively) o-r Documents/*

Question 17

Change owner

Answer 17

chown

change group ownership:
chown :Research reports.txt

chgrp Research new_reports.txt

change owner of /dir and subfiles to avance:
chown -R (recursively) avance /dir

Question 18

SUID

Answer 18

Files with s in x permission in user column
4
chmod 4764 test.sh
chmod u-s test.sh- remove

Question 19

SGID

Answer 19

Files and dirs with s permission x in group column
2
chmod -R 2764 /srv/programs/
chmod -R g-s /srv/programs/ -remove

Question 20

Sticky bit

Answer 20

Files and dirs with t in x permissions of others column
1
chmod 1777 /srv/sticky/

Question 21

List file attributes

Answer 21

lsattr ../

lsattr ./

Question 22

Change immutability of file

Answer 22

chattr -R[recurcively] -i myfile (remove attr)

chattr +i myfile (add attr)

Question 23

Turn on/off deletion attr of file

Answer 23

chattr +u myfile

chattr -u myfile

Question 24

umask

Answer 24

/etc/bashrc
The value which will be subtracted from default permissions:
777=default for dirs
666=default for files 
\_\_\_
umask u=rwx,g=,o=
=> umask value=0077
\_\_\_\_

Question 25

File access control lists

Answer 25

getfacl myfile
 user::rw-
 group::r--
 others::---
setfacl -m u:jimmy:r myfile
setfacl -x g:staff file1 -remove facl for group staff from file1