umask

Set default permissions mask for newly created files and directories.

low risk

interactive breakdown — edit the command and press Explain
$ 
What it does

umask defines which permission bits are removed from new files/directories. The default umask 022 means files are created 644 (666-022) and directories 755 (777-022). A stricter umask 027 gives 640/750 — better for multi-user servers.

Common flags
FlagMeaning
-S --symbolicDisplay mask in symbolic notation
Examples
umaskDisplay current umask in octal · explain & risk-check →
umask -SDisplay current umask symbolically · explain & risk-check →
umask 027New files: owner rw, group r, others none · explain & risk-check →
umask 077New files: owner rw only — maximum privacy · explain & risk-check →
Pro tip

Set umask 027 in /etc/profile.d/ for service accounts on production servers — prevents world-readable files from being created accidentally.

Related
chmod chown stat
Open the full explainer →More in Users, Permissions & Security

Reference text is hand-written and may be incomplete — check man umask for your version. Test destructive commands on a non-production system first.