Linux 9
Server setup and day-to-day commands by distribution and version, with the output they print.
- Check how much disk the systemd journal uses and shrink it
Check how much disk the journal uses, delete old files with vacuum, pin a size limit with a drop-in file, and find the units that fill the journal.
Ubuntu 24.04 · systemd 255 · settings per freedesktop.org journald.conf(5) and journalctl(1) - Find what is using the space when a disk is full
Find the full file system with df, narrow down big files with du and find, then handle space that does not come back after a delete and inode exhaustion.
Ubuntu 24.04.5 LTS · coreutils 9.4 · lsof 4.95.0 · ext4 loop file system - Find why a systemd service is failed
Read the Active and status lines of systemctl status, check the log from just before the failure, and fix 203/EXEC and "start request repeated too quickly".
Ubuntu 24.04 · systemd 255 (reproduced with transient units) - Fix "Could not calculate the upgrade" on Ubuntu 24.04 to 26.04
Diagnose "Could not calculate the upgrade" when moving from Ubuntu 24.04 to 26.04, then clear held packages, broken dependencies and conflicting PPAs.
Ubuntu 24.04 → 26.04 · Ubuntu docs and Launchpad reports, 2026-10 - Fix Nginx proxy blocked by SELinux on Rocky Linux 9
Tell whether a 502 and a Permission denied in error.log come from SELinux, fix it with a boolean, and label a custom document root.
Rocky Linux 9 · per RHEL 9 SELinux documentation · 2026-10 - Install Nginx and set the server name
Install Nginx from the Ubuntu repository, set the default site to your host name, then test the config and reload without dropping connections.
Ubuntu 24.04.5 LTS · nginx 1.24.0 - Put Nginx in front of an app as a reverse proxy
Send one host name to an app on a local port, pass the client address along, and tell a proxy 502 apart from an app error.
Ubuntu 24.04.5 LTS · nginx 1.24.0 · Python 3 http.server (test app) - See which process is listening on a port
List listening TCP sockets with their processes, narrow to one port, and check that firewalld lets that port through.
ss (iproute2) · Ubuntu 24.04 output · firewalld per RHEL 9 and firewalld docs (same family as Rocky 9) - Write a logrotate config and test it before using it
Write a logrotate config for an app log, preview it with -d, force a run with -f and a state file, and check the result. Covers copytruncate versus postrotate.
logrotate 3.21.0 · Ubuntu 24.04 · systemd 255