Master these fundamental commands that form the backbone of daily administration:

# Process management
ps aux | grep [process]
kill -9 [PID]
systemctl status|start|stop|restart [service]
journalctl -xe

# File operations
grep -r "pattern" /path/
find / -name "filename" -type f -mtime +30
rsync -avzP source/ user@remote:dest/
chmod 755 file.sh
chown user:group file

Network troubleshooting commands you'll use constantly:

# Basic connectivity
ping -c 4 example.com
traceroute example.com
mtr example.com

# Advanced diagnostics
ss -tulnp
netstat -plant
tcpdump -i eth0 port 80
nmap -sV 192.168.1.0/24

# Firewall management (iptables)
iptables -L -n -v
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
iptables-save > /etc/iptables.rules

Critical storage commands for daily operations:

# Disk space management
df -hT
du -sh *
lsblk
fdisk -l

# LVM operations
pvdisplay
vgdisplay
lvdisplay
lvresize -L +10G /dev/vg0/lv_root

# Mount management
mount /dev/sdb1 /mnt/data
umount -l /mnt/data
/etc/fstab entries debugging

Distribution-specific package commands:

# Debian/Ubuntu
apt update && apt upgrade
apt-cache search package
dpkg -l | grep package
apt-get install --reinstall package

# RHEL/CentOS
yum update
yum provides */command
rpm -qa | grep package
yum history undo [ID]

Essential security commands:

# User management
adduser newuser
passwd -l username
chage -l username
visudo

# SSH security
ssh-keygen -t rsa -b 4096
ssh-copy-id user@remote
/etc/ssh/sshd_config modifications:
  PermitRootLogin no
  PasswordAuthentication no

Key services every admin should know:

# Apache/Nginx
apachectl configtest
nginx -t
grep -r "DocumentRoot" /etc/apache2/

# Database (MySQL/MariaDB)
mysql -u root -p
SHOW PROCESSLIST;
GRANT ALL PRIVILEGES ON db.* TO 'user'@'localhost';

# Samba shares
smbclient -L //server -U user
testparm -s

Common scripting patterns:

#!/bin/bash
# Backup script example
DATE=$(date +%Y%m%d)
mysqldump -u root -p database > /backups/db_$DATE.sql
tar -czf /backups/web_$DATE.tar.gz /var/www/
find /backups/ -type f -mtime +30 -delete

Quick problem-solving commands:

# System logs
tail -f /var/log/syslog
dmesg | grep -i error

# Performance
top
htop
iotop
iftop
vmstat 1 10

---

Understanding Linux file systems and permissions is fundamental. You should be able to:

# Check disk usage
df -h
du -sh *

# Modify permissions
chmod 755 /path/to/file
chown user:group /path/to/file

# Find files with specific permissions
find / -type f -perm 4000 -ls

Different distributions use different package managers:

# Debian/Ubuntu
apt update
apt install package
apt remove package

# RHEL/CentOS
yum install package
dnf remove package

# Arch
pacman -S package
pacman -R package

Network configuration and troubleshooting:

# Check network interfaces
ip a
ifconfig

# Test connectivity
ping google.com
traceroute google.com

# Check open ports
netstat -tulnp
ss -tulnp

Monitoring and controlling processes:

# View running processes
top
htop
ps aux

# Kill processes
kill -9 PID
pkill process_name

Working with system services:

# Systemd commands
systemctl start service
systemctl stop service
systemctl enable service
journalctl -u service -f

Basic security practices:

# Firewall management
ufw allow 22/tcp
iptables -L

# SSH configuration
vim /etc/ssh/sshd_config
ssh-keygen -t rsa

Working with system logs:

# View logs
tail -f /var/log/syslog
journalctl -xe

# Search logs
grep "error" /var/log/messages

Automating tasks with scripts:

#!/bin/bash
# Backup script example
backup_dir="/backups"
mkdir -p $backup_dir
tar -czf $backup_dir/backup_$(date +%Y%m%d).tar.gz /path/to/backup
find $backup_dir -type f -mtime +30 -delete

Working with Apache/Nginx:

# Apache virtual host
<VirtualHost *:80>
    ServerAdmin webmaster@example.com
    DocumentRoot /var/www/example.com
    ServerName example.com
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

# Nginx server block
server {
    listen 80;
    server_name example.com;
    root /var/www/example.com;
    index index.html;
}

Basic MySQL/MariaDB operations:

# Login to MySQL
mysql -u root -p

# Common commands
CREATE DATABASE dbname;
GRANT ALL PRIVILEGES ON dbname.* TO 'username'@'localhost';
FLUSH PRIVILEGES;

Scheduling tasks:

# Edit crontab
crontab -e

# Example entries
0 3 * * * /path/to/backup.sh
*/15 * * * * /path/to/monitor.sh

System performance checks:

# CPU usage
mpstat 1 5

# Memory usage
free -m
vmstat 1 5

# Disk I/O
iostat -x 1 5

Quick fixes for common problems:

# Disk full issues
du -sh * | sort -h
find / -type f -size +100M -exec ls -lh {} \;

# High load
uptime
ps aux --sort=-%cpu | head