RTFM · Tools
Permissions, processes and logs in practice
Beyond definitions: how permissions, processes and logging interlock during real diagnostics, and the handful of idioms covering most situations.
Permission triage
id # whoami effectively
namei -l /path/to/stuck/file # per-component perms
stat file # full metadataFix ownership before modes when a copy operation imported the wrong user; guessing chmod masks the real fault.
Process inspection ladder
ps aux | grep -v grep | grep nginx
pgrep -af nginx
vmstat 1 5 # sampled pressure
free -m # memory
uptime # load contextkill -9 as opening move skips the daemon's chance to flush state politely. SIGTERM first; escalate only if genuine unresponsiveness is proven after patience.
Logs as investigation material
Identify the active log sink, then master fewer tools deeply.
tail -f /var/log/messages # follow live
less +F critical.log # forward-scrolling viewer
zgrep ERROR rotated.log.gz # search compressed historyEstablish rotation habits deliberately via logrotate configuration matched to retention norms and disk capacity, checked quarterly. Unbounded growth equals scheduled outage.
Cross-cutting example
# Diagnose HTTP service acting strange:
pgrep -af haproxy
tail -n100 /var/log/haproxy.log
ss -tlnp | grep -E ':443|:80'
namei -l /etc/haproxy/haproxy.cfg # cert/config readable?Prove it works: unified diagnostic fluency
arbitrary misbehaving service gets examined along identity→process→resource→log axes without handbook references.
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