LINUX ADMINISTRATION SKILLS

LINUX ADMINISTRATION SKILLS FOR USER, NETWORK, and SERVICES

1. USER ADMINISTRATION

User Management

Command	Description
sudo useradd -m username	Create a new user
sudo passwd username	Set user password
sudo usermod -aG group username	Add user to group
sudo usermod -L username	Lock user account
sudo usermod -U username	Unlock user account
sudo userdel -r username	Delete user with home

Group Management

Command	Description
sudo groupadd groupname	Create a new group
sudo groupdel groupname	Delete a group
groups username	Show user's groups
sudo gpasswd -d username group	Remove user from group

Permissions

Command	Description
ls -l	List permissions
chmod 755 file	Change permissions
chown user:group file	Change owner and group
chown -R user:group /dir	Change owner recursively

Privilege / Sudo

Command	Description
sudo -l	List sudo privileges
sudo visudo	Edit sudoers file safely
sudo -u user command	Run command as another user
sudo -i	Switch to root user

Important Files

• /etc/passwd — User account information
• /etc/shadow — Password hashes
• /etc/group — Group information
• /etc/sudoers — Sudo configuration
• /etc/hosts — Hostname mapping
• /etc/ssh/sshd_config — SSH server configuration

2. NETWORK ADMINISTRATION

IP & Interface Management

Command	Description
ip addr	Show all IP addresses
ip link	Show interface status
sudo ip link set eth0 up	Bring interface up
sudo ip link set eth0 down	Bring interface down
sudo ip addr add 192.168.1.100/24 dev eth0	Add IP address
sudo ip addr del 192.168.1.100/24 dev eth0	Remove IP address

Routing

Command	Description
ip route	Show routing table
sudo ip route add default via 192.168.1.1	Add default gateway
sudo ip route add 10.10.0.0/16 via 192.168.1.1	Add route
sudo ip route del 10.10.0.0/16	Delete route

Network Testing

Command	Description
ping 8.8.8.8	Test connectivity
nslookup google.com	DNS lookup
dig google.com	DNS query (detailed)
curl -I https://example.com	Test HTTP/HTTPS
traceroute 8.8.8.8	Trace network path

Network Utilities

Command	Description
ss -tuln	Show listening ports
ss -tulpn	Show ports with process
nc -zv 192.168.1.10 80	Test TCP port
nmcli device status	Show network devices
nmcli connection show	Show connections

Important Files

• /etc/resolv.conf — DNS configuration
• /etc/hosts — Local hostname mapping
• /etc/hostname — System hostname
• /etc/network/ — Network configuration files
• /etc/sysconfig/network-scripts/ — Network scripts (RHEL/CentOS)

3. SERVICES ADMINISTRATION

Service Management (systemd)

Command	Description
systemctl status service	Check service status
sudo systemctl start service	Start service
sudo systemctl stop service	Stop service
sudo systemctl restart service	Restart service
sudo systemctl reload service	Reload service
sudo systemctl enable service	Enable at boot
sudo systemctl disable service	Disable at boot
sudo systemctl enable --now service	Enable and start

Service Information

Command	Description
systemctl is-active service	Check if running
systemctl is-enabled service	Check if enabled
systemctl --type=service --state=running	List running services
systemctl --failed	List failed services

Logs (journalctl)

Command	Description
journalctl -u service	Logs of a service
journalctl -u service -f	Follow logs live
journalctl -b	Logs since boot
journalctl -b -1	Logs from previous boot

Process Management

Command	Description
ps aux	Show all processes
top / htop	Monitor processes
pgrep process	Find process ID
kill PID	Kill process
pkill process	Kill by name

Package Management

For Debian / Ubuntu (APT)

Command	Description
sudo apt update	Update repositories
sudo apt upgrade	Upgrade packages
sudo apt install package	Install package
sudo apt remove package	Remove package

For RHEL / CentOS / Rocky (DNF)

Command	Description
sudo dnf update	Update repositories
sudo dnf install package	Install package
sudo dnf remove package	Remove package
sudo dnf search package	Search package