CHEAT SHEET – Linux

Permission number (octal mode)

User | Group | Other

Permission Set	Octal value
—	0
–x	1
-w-	2
-wx	3
r–	4
r-x	5
rw-	6
rwx	7

Get octal format of myfile permission:

stat -c '%a' myfile

User management

• Could check the count of users in /home directory! but not accurate as differs from distros 🙂
• Manage users via:

/etc/passwd

• First user usually gets UID=1000.
• UIDs <1000 are system user accounts.
• Count number of users:

sudo cat /etc/passwd | wc -l

• Search user michael:

sudo cat /etc/passwd | grep michael

• Add user (with explicit home folder)

sudo adduser -m john

• Ubuntu

sudo adduser --home /home/mika --shell /bin/bash mika

• Remove user with home folder (would depend on retention policy..)

sudo userdel -r john

• Set password for specific user

sudo passwd bill

• System user (for automation/cron) -r

sudo user add -r sysuser

• Passwords in

sudo nano /etc/shadow

User default Shell

• List available shells

cat /etc/shells

• Set shell for new users in:

/etc/default/useradd

• Manually change it /etc/passwd file

sudo nano /etc/passwd

• usermod – (user modifying) eg: /bin/sh to /bin/bash

grep john /etc/passwd
usermod --shell /bin/bash john

• chsh – (change shell) eg: /bin/bash to /bin/sh

grep john /etc/passwd
chsh --shell /bin/sh john

Links (symbolic & hard)

• link object to another
• inode (ls -i): data object that contains metadata about the files (incl. size, owner, permission string..)

ln -

Trash location

/home/$USER/.local/share/Trash
/home/ubuntu/.local/share/Trash

sudo cd /root/.local/share/Trash

scp

Secure Copy Protocol – copy files/folders:

• between local host and remote host
• between 2 remote hosts

sudo scp -i /home/ubuntu/mikado/Keypair.pem -r /home/ubuntu/mikado ubuntu@1.2.3.4:/home/ubuntu/mikado

File

Copy file from local to a host

scp file.txt username@to_host:/remote/directory/

Copy file from remote to local

scp username@from_host:file.txt /local/directory/

 Directory

Copy directory from local to remote

scp -r /local/directory/ username@to_host:/remote/directory/

Copy directory from remote to local

scp -r username@from_host:/remote/directory/  /local/directory/

Remote to remote

Copy file from remote host to remote host

scp username@from_host:/remote/directory/file.txt username@to_host:/remote/directory/

find

sudo find / -type f -name '*.pem'

sudo find / -type d -name '*ssl*'

environment variables

env

printenv

Datas streams

STDIN	0
STDOUT	1
STDERR	2

find /etc -type f 1>fin_results.txt 2>find_errors.txt