Tag: sysadmin

ss replaces netstat on modern Linux: faster, shows more socket detail, and reads from the kernel. Every netstat command you rely on, rewritten for ss.

docker system prune reclaims space and can delete volumes you wanted. What each cleanup command removes, how to check usage first, and a safe script.

Cron runs a different PATH, mutes stdout, and breaks MAILTO quietly. Absolute paths, an explicit PATH, log redirection, and how to test a job first.

Why Linux kills your app with no warning. Understand the OOM killer, read dmesg logs, and shield critical processes with oom_score_adj and swap.

Master ~/.ssh/config: Host aliases, HostName, User, Port, IdentityFile, ProxyJump. Stop typing long SSH commands. One-line setup.

The latest tag does not mean newest, it means whatever was pushed untagged. Why that breaks reproducible deploys and how to pin versions and digests.

kill -9 skips cleanup and leaves locks and half-written data behind. SIGTERM vs SIGKILL, the graceful shutdown pattern, pkill, and how systemd does it.

Understand Linux umask: what it is, how 022 and 027 work, calculating file permissions, and why it matters for shared directories and security.

The /proc filesystem is a live window into every running process on Linux. Debug PIDs, file descriptors, memory, and limits with no extra tools installed.

Compare zram (compressed RAM) and traditional swap files. Learn when each works, setup, and real-world performance trade-offs for memory-constrained systems.

Use strace to trace system calls and debug mysterious permission errors, missing files, and network issues without ever reading source code.

lsof shows every open file, socket, and port on the box. Find what holds a port, trace deleted files still eating disk, and see what a service owns.