Most Common chmod File Permissions (Linux Admin)

Here are the most frequent chmod file permission commands used by Linux admins:

1. chmod 644 file.txt

  • Owner: read + write
  • Group: read
  • Others: read
-rw-r--r--
Used for regular files (e.g., text, config files). Prevents unauthorized edits—only the owner can modify, but all can read.

2. chmod 755 script.sh

  • Owner: read + write + execute
  • Group: read + execute
  • Others: read + execute
-rwxr-xr-x
Used for scripts or binaries. Owner can edit and execute; others can execute but not modify.

3. chmod 700 private.key

  • Owner: read + write + execute
  • Group: none
  • Others: none
-rwx------
Used for highly sensitive files or private SSH keys. Only the owner has any permissions.

Other Useful Examples

  • chmod 600 secret.txt: Owner can read/write, no permissions for anyone else.
  • chmod 777 public_dir: Everyone can read/write/execute (usually discouraged for security reasons).

Symbolic (Human-Readable) Changes

chmod u+x script.sh    # Add execute for owner
chmod go-w file.txt    # Remove write for group and others
chmod a+r file.txt     # Give everyone read
Tip: Use numeric mode (chmod 755) for quick changes; symbolic mode (chmod u+x) for fine control.
(Sources: linuxize.com, redhat.com, strongdm.com)