Linux Gotchas

Permission Traps

• chmod 777 fixes nothing, breaks everything — find the actual owner/group issue
• Setuid on scripts is ignored for security — only works on binaries
• chown -R follows symlinks outside target directory — use --no-dereference
• Default umask 022 makes files world-readable — set 077 for sensitive systems
• ACLs override traditional permissions silently — check with getfacl

Process Gotchas

• kill sends SIGTERM by default, not SIGKILL — process can ignore it
• nohup doesn't work if process already running — use disown instead
• Background job with & still dies on terminal close without disown or nohup
• Zombie processes can't be killed — parent must call wait() or be killed
• kill -9 skips cleanup handlers — data loss possible, use SIGTERM first