Master Essential Linux Commands: From ls to chmod Explained

Linux offers a rich set of command‑line tools that are essential for file management, system navigation, and administration. Below is a concise reference for the most commonly used commands.

1. ls command

The ls command lists directory contents and can display file permissions, owners, and timestamps. ls -a – list all files, including hidden ones starting with

.

ls -A

– list all except . and

..

ls -r

– reverse order ls -t – sort by modification time ls -S – sort by size ls -h – human‑readable sizes ls -l – detailed list with permissions, owners, etc.

Examples: ls -lhrt – human‑readable, reverse time order with details ls -lrS – size‑sorted reverse order with details ls -l t* – detailed list of entries starting with “t” ls | sed "s:^:`pwd`/:" – prepend absolute path (excluding hidden files) find $pwd -maxdepth 1 | xargs ls -ld – list absolute paths including hidden files

2. cd command

cd

(change directory) switches the current working directory. cd / – go to root cd ~ – go to home directory cd - – return to previous directory cd !$ – use the last argument of the previous command as the target

3. pwd command

pwd

prints the current working directory. pwd – show current path pwd -P – show the physical path, resolving symlinks

4. mkdir command

mkdir

creates new directories. -m – set access mode (permissions) at creation -p – create parent directories as needed

Examples: mkdir t – create directory t in the current location mkdir -p /tmp/test/t1/t – create nested path, creating missing parents

5. rm command

rm

removes files or directories. Use -r to delete directories recursively. rm -i *.log – interactively delete all .log files rm -rf test – forcefully delete directory test and its contents rm -- -f* – delete files whose names start with

-f

6. rmdir command

rmdir

removes empty directories. rmdir -p parent/child/child11 – remove the specified directory and its empty ancestors

7. mv command

mv

moves or renames files. mv test.log test1.txt – rename file mv llog1.txt log2.txt log3.txt /test3 – move multiple files to

/test3

mv -i log1.txt log2.txt

– interactive overwrite prompt mv * ../ – move all files in the current directory up one level

8. cp command

cp

copies files or directories. cp -ai a.txt test – copy a.txt to test preserving timestamps and prompting before overwrite cp -s a.txt link_a.txt – create a symbolic link named

link_a.txt

9. cat command

cat

concatenates and displays file contents. cat filename – display entire file cat > filename – create a new file from keyboard input cat file1 file2 > file – merge files into a new file cat -n log2012.log log2013.log – add line numbers to output cat -b log2012.log log2013.log log.log – number non‑blank lines

cat >log.txt <<EOF
Hello
World
PWD=$(pwd)
EOF

– here‑document example tac log.txt – display file in reverse order

10. more command

more

paginates output, allowing forward navigation. more +3 text.txt – start display at line 3 ls -l | more -5 – show 5 lines per page

Key bindings: Space – next page, b – previous page, q – quit

11. less command

less

provides bidirectional pagination and searching. less -i – ignore case in searches less -N – show line numbers /pattern – search forward, ?pattern – search backward n / N – repeat last search forward/backward ps -aux | less -N – view process list with line numbers less 1.log 2.log – view multiple files

12. head command

head

outputs the beginning of a file (default first 10 lines). head 1.log -n 20 – first 20 lines head -c 20 log2014.log – first 20 bytes head -n -10 t.log – last 10 lines

13. tail command

tail

outputs the end of a file and can follow updates. tail -f ping.log – continuously display new lines as the file grows tail -n 20 file.log – last 20 lines

14. which command

which

locates the executable file associated with a command in the PATH. which ls – show path of

ls

which cd

– reports not found because cd is a shell builtin echo $PATH – display current PATH variable

15. whereis command

whereis

searches for binaries, sources, and manuals. whereis locate – locate binary, source, and man page whereis -s locate – source only whereis -m locate – manual only

16. locate command

locate

queries a prebuilt database for fast filename searches. locate pwd – find files containing “pwd” in their names locate /etc/sh – find files in /etc starting with “sh” locate -r '^/var.*reason$' – regex search for paths ending with “reason” under

/var

17. find command

find

searches directory trees for files matching criteria. find -atime -2 – files accessed within the last 48 hours find ./ -name '*.log' – .log files in current directory find /opt -perm 777 – files with permission 777 find -size +1000c – files larger than 1000 bytes find . -type f -mtime +10 -exec rm -f {} \; – delete files older than 10 days without prompt find . -name '*.log' -exec cp {} test3 \; – copy all .log files to

test3

find . -type f -print | xargs file

– determine file types via

xargs

18. chmod command

chmod

changes file or directory permissions. chmod a+x t.log – add execute permission for all users chmod u=r t.log -c – set owner read‑only and report changes chmod 751 t.log – owner rwx, group r‑x, others x chmod u+r,g+r,o+r -R text/ -c – add read permission recursively

19. tar command

tar

creates and extracts archive files; compression is delegated to other utilities. tar -cvf log.tar 1.log 2.log – create archive tar -zcvf /tmp/etc.tar.gz /etc – create gzip‑compressed archive of

/etc

tar -ztvf /tmp/etc.tar.gz

– list contents of gzip archive tar --exclude /home/dmtsai -zcvf myfile.tar.gz /home/* /etc – archive while excluding a path

20. chown command

chown

changes file ownership. chown -c mail:mail log2012.log – change owner and group, show changes chown -c :mail t.log – change group only chown -cR mail: test/ – recursively change owner and group of a directory

These commands form the backbone of everyday Linux system usage, enabling efficient file handling, permission management, and system navigation.