Master Essential Linux Commands: From Navigation to File Management

1. Common Commands

1. Directory operation commands

1.1.1 ls command

ls is the most common directory operation command, used to list the contents of a directory.

Command name: ls

English meaning: list

Location: /bin/ls

Description: display directory contents

Code:

# ls [options] [filename or directory name]
-a    show all files
--color=when    support colored output, when defaults to always (always show color), can be never or auto
-d    show directory information, not the files inside
-h    human‑readable format
-i    show inode number
-l    long format display

Demo:
# ls -l
total 16
drwxr-xr-x. 2 root root 29 Dec 23 11:24 123
-rw-------. 1 root root 1687 Nov 25 21:49 anaconda-ks.cfg
...

1.1.2 cd command

cd changes the current directory.

Command name: cd

English meaning: change directory

Location: built‑in shell command

Permissions: all users

Description: switch current directory

# cd [filename or directory name]
~    home directory
-    previous directory
.    current directory
..   parent directory

1.1.3 Absolute and relative paths

Absolute path: starts from the root directory.

Relative path: based on the current directory.

1.1.4 pwd command

pwd prints the current working directory.

Command name: pwd

English meaning: print working directory

Location: /bin/pwd

Permissions: all users

Description: query current directory

1.1.5 mkdir command

mkdir creates a directory.

Command name: mkdir

English meaning: make directory

Location: /bin/mkdir

Permissions: all users

Description: create empty directory

# mkdir [options] directory_name
Options:
-p    create parent directories as needed

1.1.6 rmdir command

rmdir removes an empty directory.

Command name: rmdir

English meaning: remove directory

Location: /bin/rmdir

Permissions: all users

Description: delete empty directory

# rmdir [options] directory_name
Options:
-p    remove parent directories recursively

2. File operation commands

1.2.1 touch command

touch creates an empty file or updates its timestamps.

Command name: touch

English meaning: change file timestamps

Location: /bin/touch

Permissions: all users

Description: create empty file or modify timestamps

# touch filename

1.2.2 stat command

stat displays detailed file information, including three timestamps.

Command name: stat

English meaning: display file or file system status

Location: /bin/stat

Permissions: all users

Description: show file details

# stat b1001
File: "b1001"
Size: 41   Blocks: 8   IO Block: 4096   regular file
Device: 803h/2051d   Inode: 33582185   Links: 1
Access: (0644/-rw-r--r--)  Uid: (0/ root)   Gid: (0/ root)
...

1.2.3 cat command

cat concatenates files and prints to standard output.

Command name: cat

English meaning: concatenate files and print on the standard output

Location: /bin/cat

Permissions: all users

Description: display file contents

# cat [options] filename
Options:
-A    show all hidden characters
-E    display $ at end of each line
-n    show line numbers
-T    display tabs as ^I
-v    show non‑printing characters

1.2.4 more command

more displays file contents page by page.

Command name: more

English meaning: file perusal filter for CRT viewing

Location: /bin/more

Permissions: all users

Description: paginate file display

more opens an interactive page
Space    next page
b        previous page
Enter    scroll one line
/str     search string
q        quit

1.2.5 less command

less is similar to more but allows backward movement.

Command name: less

English meaning: opposite of more

Location: /bin/less

Permissions: all users

Description: view file contents with scrolling

1.2.6 head command

head shows the beginning of a file.

Command name: head

English meaning: output the first part of files

Location: /usr/bin/head

Permissions: all users

Description: display file header

# head -n 19 anaconda-ks.cfg
#version=DEVEL
# System authorization information
auth --enableshadow --passalgo=sha512
...

1.2.7 tail command

tail shows the end of a file.

Command name: tail

English meaning: output the last part of files

Location: /usr/bin/tail

Permissions: all users

Description: display file tail

Options:
-n    number of lines from end
-f    follow file as it grows

1.2.8 ln command

ln creates links between files.

Command name: ln

English meaning: link

Location: /bin/ln

Permissions: all users

Description: create hard or symbolic links

# ln [options] source_file target_file
Options:
-s    create symbolic link
-f    force, remove existing target

3. Commands usable on both files and directories

1.3.1 rm command

rm removes files or directories.

Command name: rm

English meaning: remove file or directory

Location: /bin/rm

Permissions: all users

Description: delete files or directories

# rm [options] file_or_directory
Options:
-r    recursive delete, can remove directories
-f    force delete
-i    interactive delete

1.3.2 cp command

cp copies files or directories.

Command name: cp

English meaning: copy file or directory

Location: /bin/cp

Permissions: all users

Description: duplicate files or directories

# cp [options] source_file target_file
Options:
-a    same as -dpr (archive)
-d    if source is a symlink, create symlink
-i    prompt before overwrite
-p    preserve attributes
-r    recursive copy

1.3.3 mv command

mv moves or renames files.

Command name: mv

English meaning: move (rename) files

Location: /bin/mv

Permissions: all users

Description: move or rename files

# mv [options] source_file target_file
Options:
-f    force overwrite
-d    interactive move
-v    verbose output

4. Basic permission management

1.4.1 chmod command

chmod changes file mode bits.

Command name: chmod

English meaning: change file mode

Location: /bin/chmod

Permissions: all users

Description: modify file permission mode

# chmod [options] mode file
Options:
-R    recursive change

1.4.2 Permission modes

chmod mode format: [ugoa][+-=][perms] where u=user, g=group, o=others, a=all.

+ adds permission, - removes, = sets exactly.

Permissions: r=read, w=write, x=execute.

1.4.3 Numeric permissions

4=read, 2=write, 1=execute.

Owner and group commands

1.4.4 chown command

chown changes file owner and group.

Command name: chown

English meaning: change file owner and group

Location: /bin/chown

Permissions: all users

Description: modify owner or group of a file or directory

# chown [options] owner:group file_or_directory
Options:
-R    recursive

1.4.5 chgrp command

chgrp changes the group ownership.

Command name: chgrp

English meaning: change group ownership

Location: /bin/chgrp

Permissions: all users

Description: modify group of a file or directory

# chgrp [options] group file_or_directory

umask default permissions

5. Help commands

1.5.1 man command

man displays the manual pages.

Command name: man

English meaning: manual

Location: /usr/bin/man

Permissions: all users

Description: show online help manual

# man [options] command
Options:
-f    show which help level a command has
-k    search related help topics

Shortcut

Function

Up Arrow

move up one line

Down Arrow

move down one line

PgUp

page up

PgDn

page down

g

go to first page

G

go to last page

q

quit

/string

search forward

?string

search backward

n

next match

N

previous match

Man help level image:

1.5.2 info command

info provides GNU info manuals.

1.5.3 help command

help shows help for shell built‑in commands.

Command name: help

English meaning: help

Location: built‑in shell command

Permissions: all users

Description: display help for built‑in commands

1.5.4 --help option

Most commands support the --help option to display usage information.

6. Search commands

1.6.1 whereis command

whereis locates the binary, source, and manual page files for a command.

Command name: whereis

English meaning: locate the binary, source, and manual page files for a command

Location: /usr/bin/whereis

Permissions: all users

Description: find binary, source, and documentation

1.6.2 which command

which shows the full path of a command and can reveal aliases.

Command name: which

English meaning: shows the full path of (shell) commands

Location: /usr/bin/which

Permissions: all users

Description: display command path

1.6.3 locate command

locate searches for files by name using a database.

Advantages: fast, low resource, database at /var/lib/mlocate/mlocate.db, updated with updatedb.

Disadvantage: can only search by filename.

1.6.4 find command

find searches for files in a directory hierarchy.

Command name: find

Location: /bin/find

Permissions: all users

Description: search files

Search by name:

# find path [options] pattern
-name    name (case‑sensitive)
-iname   name (case‑insensitive)
-inum    inode number

Search by size:

# find path -size [+|-]size
+    larger than size
-    smaller than size
Units: b (512‑byte blocks), c (bytes), k (KB), w (two‑byte words)

Search by time:

-atime [+|-]days   access time
-mtime [+|-]days   modification time
-ctime [+|-]days   status change time

Search by permission:

-perm mode        exact match
-perm -mode       all bits of mode set
-perm +mode       any of the bits in mode set

Search by owner/group:

-uid uid          owner uid
-gid gid          group gid
-user name        owner name
-group name       group name
-nouser           files without owner

Search by type:

-type d    directories
-type f    regular files
-type l    symbolic links

Logical operators:

-a    and
-o    or
-not  not

Other options:

-exec command {} \;   execute command on each match
-ok command {} \;      like -exec but asks for confirmation

1.6.5 grep command

grep searches for patterns in files.

# grep [options] "search pattern" filename
Options:
-i    ignore case
-n    show line numbers
-v    invert match
--color=auto   highlight matches

1.6.6 Pipe operator

Command1 | Command2 passes the output of Command1 as input to Command2.

1.6.7 Command aliases

# alias            list aliases
# alias ser='systemctl start network'   define alias

1.6.8 Common shortcuts

Shortcut

Function

TAB

auto‑complete

CTRL+A

move cursor to start of line

CTRL+E

move cursor to end of line

CTRL+C

interrupt current command

CTRL+U

cut line before cursor

CTRL+L

clear screen

CTRL+Y

paste after CTRL+U

7. Compression commands

1. zip format

zip creates zip archives, compatible with Windows.

Command name: zip

English meaning: package and compress files

Location: /usr/bin/zip

Permissions: all users

Description: compress directories or files

# zip [options] archive_name files
Options:
-r    recurse into directories

1.2 unzip format

unzip extracts zip archives.

Command name: unzip

Location: /usr/bin/unzip

Permissions: all users

Description: decompress zip files

# unzip [options] archive.zip
Options:
-d    extract to directory

2. gz format

gzip compresses files; gunzip or gzip -d decompresses.

# gzip [options] file
Options:
-c    write to stdout, keep original
-d    decompress
-r    compress directories

4. tar format

tar creates and extracts archive files.

Command name: tar

Location: /bin/tar

Permissions: all users

Description: pack and unpack archives

# tar [options] [-f archive] files
Options:
-c    create
-f    archive file name
-v    verbose
-x    extract
-t    list contents
-C    change to directory before operation
-z    handle .tar.gz
-j    handle .tar.bz2

8. Shutdown and reboot

1. sync command

sync flushes file system buffers.

Command name: sync

English meaning: flush file system buffers

Location: /bin/sync

Permissions: all users

Description: synchronize cached writes to persistent storage

2. shutdown command

shutdown brings the system down.

Command name: shutdown

English meaning: bring the system down

Location: /sbin/shutdown

Permissions: superuser

Description: power off or reboot

# shutdown [options] time [message]
Options:
-c    cancel a pending shutdown
-h    halt
-r    reboot

3. reboot command

# reboot   # restart the system

4. halt and poweroff commands

halt and poweroff immediately power off the machine; they do not gracefully stop services.

# halt
# poweroff

5. init command

# init 0   # halt (runlevel 0)
# init 6   # reboot (runlevel 6)