Linux Troubleshooting

Quick Checklist

The System Is Slow

uptime
top
htop
free -h
vmstat 1
iostat
df -h
du -sh /var/*

Look at:

• load average
• CPU steal or iowait
• memory and swap
• disk usage and inode exhaustion

A Service Does Not Start

systemctl status myapp
journalctl -u myapp -xe
systemctl cat myapp
ss -tulpn

Check:

• the unit file
• permissions on the binary and directories
• whether the port is already in use
• whether the config is valid

There Is Not Enough Disk Space

df -h
df -i
du -xhd1 /
journalctl --disk-usage
find /var/log -type f -size +100M

High Load

Separate:

• CPU saturation
• disk I/O wait
• memory pressure
• hung NFS or network storage

Practice

• Do not start with a restart until you collect the basic symptoms.
• Determine first whether the issue is system-wide or limited to one service.
• Always capture the timeline: when it started and what changed before it.