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Common Commands 1 ​

MAN ​

This command can view different sections of the manual pages.

bash
man man
bash
man - an interface to the system reference manuals

The table below shows the section numbers of the manual followed by the types of pages they contain.

1 Executable programs or shell commands
2 System calls (functions provided by the kernel)
3 Library calls (functions within program libraries)
4 Special files (usually found in /dev)
5 File formats and conventions, e.g. /etc/passwd
6 Games
7 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
8 System administration commands (usually only for root)
9 Kernel routines [Non standard]

Section ​

bash
man 1 ls/cp/mv
man 2 write/open/close
man 3 printf/malloc/free
man 4 tty/null/random
man 5 passwd/fstab
man 7 man
man 8 ifconfig/iptables/mount
man 9 fork # not work

Games ​

fortune can randomly display quotes and jokes.

bash
apt install fortune/fortune-mod/fortunes-zh
bash
man 6 fortune
bash
fortune - print a random, hopefully interesting, adage

Can be combined with cowsay and lolcat to play.

bash
fortune | cowsay | lolcat

PWD ​

Print Working Directory.

bash
man pwd
bash
pwd - print name of current/working directory

CAT ​

bash
man cat
bash
cat - concatenate files and print on the standard output

Line No. With Blank Lines ​

bash
cat -n FILE

Line No. Without Blank ​

bash
cat -b FILE

LS ​

bash
man ls
bash
ls - list directory contents

File Details ​

bash
ls -lh
bash
drwx------ 9 root root 4.0K   Aug  7 22:38 root
crw-rw-rw- 1 root tty  5,   0 Aug  7 22:33 /dev/tty
brw-rw---- 1 root disk 252, 0 Aug  7 21:30 /dev/vda
  • File type: d directory, - file, l link, c character device, b block device.
  • File permissions: 700, Owner: 7, Group: 0, Other: 0
  • Hard link count: 9
  • File owner: root
  • File group: root
  • File size: 4.0K
  • Modification time: Aug 7 22:38
  • File name: root
  • Major device number: 5/252, identifies the device driver
  • Minor device number: 0, identifies a specific device instance within the same class of devices

Only Dirs ​

bash
ls -ld */

Including hidden files

bash
ls -ld .*/ */

Specify Dir ​

bash
ls -ld /usr

Type Symbols ​

bash
ls -lF /
  • /: directory
  • *: executable file
  • @: symbolic link
  • |: named pipe
  • =: socket

Hidden Characters ​

bash
ls ~ | wc -l

There are hidden characters \n in the output of the ls command.

bash
ls ~ | od -c
bash
0000000   f   i   l   e  \n   f   o   o  \n   f   o   o   b   a   r  \n
0000020

You can also use cat -A.

bash
ls ~ | cat -A
bash
file$
foo$
foobar$

FILE ​

Show file type

bash
man file
bash
file — determine file type

Character/Block Device ​

bash
file /dev/tty
bash
/dev/tty: character special (5/0)
bash
file /dev/vda
bash
/dev/vda: block special (252/0)

Note the trailing slash.

bash
file /bin
bash
/bin: symbolic link to usr/bin
bash
file /bin/
bash
/bin/: directory

LESS ​

The more command can only load by pressing Enter, the less command is more powerful because less is more.

bash
man less
bash
less - opposite of more

USERMOD ​

bash
man usermod
bash
usermod - modify a user account

Disable Account Login ​

bash
usermod -s /sbin/nologin kuga

This command will change bin/sh to /sbin/nologin in /etc/passwd

bash
kuga:x:1000:1000::/home/kuga:/sbin/nologin

Grant User Group ​

The following command will grant the kuga user the sudo user group.

bash
usermod -aG sudo kuga

LN ​

bash
man ln
bash
ln - make links between files

go rocks

DF ​

bash
man df
bash
df - report file system disk space usage

Readable Format ​

bash
df -h

Specify File System Type ​

bash
df -h -t ext4
bash
df -h -t apfs

ext4 is the file system type of Linux, apfs is the file system type of macOS.

DU ​

Disk Usage

bash
man du
bash
du - estimate file space usage

Total Size of Dir ​

bash
du -sh ~/Downloads

Sort Files - Including Subdirs ​

bash
du -ah ~/Downloads/* | sort -rh | head -n 5
bash
du -ah ~/Downloads --max-depth=1 | sort -rh | head -n 10

Sort Files - Excluding Subdirs ​

bash
du -sh ~/Downloads/* | sort -rh | head -n 5