Change file or directory permissions
Medium risk
What do risk levels mean?
- Read-only
- Inspects state without changing anything.
- Low risk
- Reversible with a routine follow-up command.
- Medium risk
- Changes state; undo path documented.
- Destructive
- Deletes or overwrites; confirmation required.
Sets Unix permission bits on a file or directory tree — for example locking an SSH key to 600 or opening a shared directory to a group.
filespermissionschmod
Parameters
File or directory whose permissions to change.
Octal mode to apply, e.g. "600" or "755".
The mode the path had before the change (recorded in the inspect step); used only by undo.
Commands
Record the current permissions so you can restore them
ls -l "<path>"Apply the new permission mode (add -R yourself only after checking the tree)
chmod <mode> "<path>"Verification
ls -l "<path>"The permission string matches the requested mode.
Undo
Restore the mode recorded by the inspect step before the change
chmod 644 "<path>"Pitfalls
- Recursive chmod applies the same bits to files and directories; directories need x to be enterable — use "chmod -R u=rwX" style symbolic modes to set x only on directories.
- 777 is almost never the right answer; it makes the path writable by everyone.
- SSH refuses keys that are group- or world-readable; private keys should be 600.