bash
112 lines · 1 tab
Ryan Nakamura
Feb 2026
1 tab
#!/bin/bash
# Linux system administration commands
# === Process Management ===
ps aux # All processes
ps aux | grep nginx # Find specific process
top -bn1 | head -20 # Snapshot of top processes
htop # Interactive process viewer
kill -SIGTERM 1234 # Graceful stop
kill -SIGKILL 1234 # Force kill
pkill -f "node server.js" # Kill by name pattern
# === Systemd Services ===
systemctl status nginx # Service status
systemctl start nginx # Start service
systemctl stop nginx # Stop service
systemctl restart nginx # Restart service
systemctl reload nginx # Reload config
systemctl enable nginx # Enable on boot
systemctl disable nginx # Disable on boot
systemctl list-units --type=service # List all services
# === Logs (journalctl) ===
journalctl -u nginx # Service logs
journalctl -u nginx --since "1 hour ago"
journalctl -u nginx -f # Follow logs
journalctl -p err # Error priority only
journalctl --disk-usage # Log disk usage
journalctl --vacuum-size=500M # Trim logs to 500MB
# === Disk & Storage ===
df -h # Disk space usage
du -sh /var/log/* # Directory sizes
du -sh /var/log/* | sort -rh | head # Largest directories
lsblk # List block devices
mount # List mounts
findmnt -t ext4 # Find specific mounts
# Find large files
find / -type f -size +100M -exec ls -lh {} ;
# Find files modified in last 24h
find /var/log -mtime -1 -type f
# === Network ===
ss -tlnp # Listening TCP ports
ss -tunap # All connections
curl -v https://example.com # HTTP debug
dig example.com # DNS lookup
dig +short example.com A # Quick DNS
traceroute example.com # Network path
mtr example.com # Better traceroute
# Check if port is open
nc -zv hostname 443
timeout 3 bash -c 'cat < /dev/null > /dev/tcp/hostname/443' && echo "Open"
# === Users & Permissions ===
useradd -m -s /bin/bash deploy # Create user
usermod -aG sudo deploy # Add to sudo group
passwd deploy # Set password
chmod 755 /opt/app # rwxr-xr-x
chmod 600 /etc/secrets.conf # rw-------
chown -R deploy:deploy /opt/app # Change ownership
setfacl -m u:deploy:rx /var/log/app # ACL permissions
# === Performance Analysis ===
vmstat 1 5 # Virtual memory stats
iostat -x 1 5 # Disk I/O stats
sar -u 1 5 # CPU history
sar -r 1 5 # Memory history
free -h # Memory usage
uptime # Load averages
nproc # CPU count
# === Cron Jobs ===
crontab -l # List cron jobs
crontab -e # Edit cron jobs
# Cron format: minute hour day month weekday command
# 0 2 * * * /opt/scripts/backup.sh # Daily at 2 AM
# */5 * * * * /opt/scripts/health.sh # Every 5 minutes
# 0 0 * * 0 /opt/scripts/weekly.sh # Weekly on Sunday
# === Firewall (UFW) ===
ufw status verbose # Show rules
ufw allow 22/tcp # Allow SSH
ufw allow from 10.0.0.0/8 to any port 5432 # Allow DB from VPN
ufw deny 23 # Block telnet
ufw enable # Enable firewall
# === Kernel Tuning ===
sysctl -a | grep net.core # View settings
# /etc/sysctl.d/99-custom.conf
# net.core.somaxconn = 65535
# net.ipv4.tcp_max_syn_backlog = 65535
# vm.swappiness = 10
# fs.file-max = 2097152
sysctl -p /etc/sysctl.d/99-custom.conf # Apply
# === Quick Diagnostics ===
# Check why a service failed
systemctl status myapp
journalctl -u myapp --no-pager -n 50
# Check resource usage
free -h && echo "---" && df -h / && echo "---" && uptime
# Check open file limits
ulimit -n # Current limit
cat /proc/sys/fs/file-nr # System-wide file usage
1 file · bash
Explain with highlit
Linux system administration is fundamental to DevOps. Process management with ps, top, htop monitors system activity. systemctl manages systemd services—start, stop, enable, disable. Disk management with df, du, lsblk, mount handles storage. journalctl reads systemd logs with powerful filtering. Network troubleshooting uses ss, netstat, curl, dig, traceroute. User management with useradd, usermod, chmod, chown controls access. crontab schedules recurring tasks. iptables or nftables configure firewalls. sysctl tunes kernel parameters. Performance analysis with vmstat, iostat, sar identifies bottlenecks. Understanding these tools enables effective server management and troubleshooting production issues.
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