Master Essential Linux Commands for System Operations

Common Directory Commands

ls – list directory contents. Examples: ls (current directory), ls -l (long format), ls -a (include hidden files), ls -h (human‑readable sizes).

cd – change directory. Examples: cd /usr/local/src, cd ~ (home), cd - (previous), cd .. (parent).

pwd – print working directory.

Common Directories

/ – root, /bin – user‑readable commands, /boot – boot files, /dev – device files, /etc – configuration, /home – user homes, /lib – libraries, /mnt – mount points, /media – removable media, /root – root home, /tmp – temporary files, /sbin – system commands, /proc – kernel info, /sys – system info, /usr – software, /var – variable data (logs, mail, lib).

File Operations Commands

mkdir – create directories. mkdir test, mkdir -p test1/test2/test3.

rmdir – remove empty directories.

touch – create empty file or update timestamps. touch test.py.

rm – remove files or directories. rm file, rm -r dir, rm -f file, rm -rf dir.

cp – copy files or directories. cp src dest, cp -r src dest, cp -p src dest, cp -a src dest.

mv – move or rename. mv src dest, mv file /tmp/, mv file newname.

cat – display file contents. cat file, cat -n file.

more – paginate output. Use space to scroll, b to go back, q to quit.

head – show beginning of a file. head file, head -n 20 file, head -n -20 file.

ln – create links. ln -s source target creates a symbolic link.

Permission Management

File permissions are displayed as ten characters (e.g., -rw-r--r--). The first character indicates type ( - file, d directory, l link). The next nine bits represent user (u), group (g), and others (o) permissions: read (r=4), write (w=2), execute (x=1).

chmod – change mode. Symbolic: chmod u+x file, chmod g+w,o+w file, chmod u=rwx file. Numeric: chmod 755 file, chmod 644 file.

chown – change ownership. chown user file, chown user:group file.

Help Commands

man – view manual pages.

--help – display command‑specific help.

Search Commands

whereis – locate binary, source, and manual files.

find – search files. Common options: -name, -user, -group, -size, -type, -perm, -iname.

grep – search for patterns. Example: grep -i "root" /etc/passwd. Use -v to invert, -i to ignore case, and pipe ( |) to combine commands.

Compression and Decompression

Common formats: .gz, .bz2. Examples: tar -zcvf archive.tar.gz files – create gzipped tarball. tar -zxf archive.tar.gz – extract. tar -jcvf archive.tar.bz2 files – create bzip2 tarball. tar -jxf archive.tar.bz2 – extract.

Use -t to list contents without extracting.

Shutdown and Reboot Commands

shutdown – power off or reboot. shutdown -h now (halt), shutdown -r now (reboot).

reboot – immediate reboot.

Network Commands

ping – test connectivity. ping -c 4 8.8.8.8.

ifconfig – display or configure network interfaces (requires root).