Linux Survival Basics
Read-onlyFind Slow Services During Boot
A server comes back after reboot, but boot time feels long and there is no obvious culprit.
Command
systemd-analyze blame | head -20Before you run this
System impact: Read-only. Low when scoped to the shown target.
When not to use it: Do not assume the top line delayed the whole boot; follow up with systemd-analyze critical-chain.
Expected output
Startup durations sorted from slowest to fastest.
System impact
Read-only. Nothing changes. systemd prints units ordered by startup duration.
Recovery / rollback: no state is changed.
When to use it
Use after slow reboots, maintenance windows, or image changes that affect startup time.
When not to use it
Do not assume the top line delayed the whole boot; follow up with systemd-analyze critical-chain.
next steps
Related commands
Show Recent Server Reboots
Confirm whether the server actually rebooted and when.
last -x reboot | head -5
Find the Processes Using Memory
The server felt slow. Memory pressure was the first thing to rule out.
ps -eo pid,comm,%mem,%cpu --sort=-%mem | head
Find the Files Eating Your Disk
The disk was full, but guessing at folders was the slow part.
find /var -type f -printf '%s %p\n' | sort -nr | head -20
Find the Largest Installed Packages
Disk cleanup starts with evidence, not random package removal.
dpkg-query -W -f='${Installed-Size}\t${Package}\n' | sort -nr | head -20
Find the Largest CI Logs
Huge logs often point to loops, noisy tests, or runaway debug output.
find logs/ -type f -printf '%s %p\n' | sort -nr | head -10
Study mapping
Use this as independent command practice: read the notes, predict the output, then compare it with the example before using a real shell.
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.