Linux Commands:
User & Permission Commands
whoami
Description: Print current username.
Syntax: whoami
Example:
$ whoami
developer
Common flags: None.
id
Description: Show user and group IDs.
Syntax: id [USER]
Example:
$ id
uid=1000(developer) gid=1000(developer) groups=1000(developer),27(sudo)
Common flags: -u, -g, -G, -n
chmod
Description: Change file permissions.
Syntax: chmod MODE FILE
Examples:
$ chmod 644 report.txt
$ ls -l report.txt
-rw-r--r-- 1 developer developer 1234 report.txt
$ chmod u+x,g-w script.sh
$ ls -l script.sh
-rwxr--r-- 1 developer developer 4321 script.sh
Common flags: -R, --reference=FILE
chown
Description: Change file owner/group.
Syntax: chown OWNER[:GROUP] FILE
Example:
$ sudo chown bob:dev report.txt
$ ls -l report.txt
-rw-r--r-- 1 bob dev 1234 report.txt
Common flags: -R
passwd
Description: Change a user’s password.
Syntax: passwd [USER]
Example:
$ passwd
Current password:
New password:
Retype new password:
passwd: password updated successfully
Common flags: -e, -l, -u
User Group Management
Create Users
Syntax:
sudo useradd -m -s /bin/bash USER
sudo adduser USER
Example:
$ sudo useradd -m -s /bin/bash dev1
$ sudo adduser dev2
Create Groups
$ sudo groupadd developers
Add User to Group
$ sudo usermod -aG developers developer
View Groups
$ groups developer
developer : developer sudo developers
Delete Users/Groups
$ sudo userdel -r dev1
$ sudo groupdel developers
Networking Commands
ping
Example:
$ ping -c 2 8.8.8.8
2 packets transmitted, 2 received, 0% packet loss
ip / ifconfig
$ ip addr show eth0
inet 192.168.1.10/24
$ ip route
default via 192.168.1.1 dev eth0
ssh
$ ssh -i ~/.ssh/id_ed25519 -p 2222 developer@server.example.com
scp
$ scp file.txt dev@s13.221.67.64:/home/dev/demo
$ scp developer@server:/var/log/syslog ./syslog
curl
$ curl -I https://example.com
$ curl -L -o page.html https://example.com
wget
$ wget https://example.com/file.tar.gz
$ wget -c https://example.com/large.iso
Summary
- User management: whoami, id, chmod, chown, passwd\
- Group management: useradd, groupadd, usermod\
- Networking: ping, ssh, scp, sftp, curl, wget
