chmod 400
r--------, used for keys only the owner reads.
Every form
Examples
Note
Only the owner can read it, and even the owner cannot change it by accident. AWS asks for 400 on .pem key files.
Other common modes
- chmod 755
rwxr-xr-xprograms, scripts and folders - chmod 644
rw-r--r--ordinary files like web pages - chmod 600
rw-------private keys and secrets - chmod 700
rwx------private folders and scripts - chmod 777
rwxrwxrwxnothing you want to keep safe - chmod 775
rwxrwxr-xshared team folders - chmod 770
rwxrwx---folders shared with one group only - chmod 750
rwxr-x---programs for one group - chmod 744
rwxr--r--scripts only the owner runs - chmod 711
rwx--x--xhome folders you can pass through - chmod 666
rw-rw-rw-shared files, with care - chmod 664
rw-rw-r--files shared with a group - chmod 660
rw-rw----files for one group only - chmod 640
rw-r-----config the group needs to read - chmod 444
r--r--r--files nobody should change - chmod 400
r--------keys only the owner reads - chmod 4755
rwsr-xr-xprograms that run as their owner - chmod 2775
rwxrwsr-xshared folders where new files keep the group - chmod 1777
rwxrwxrwtshared temporary folders like /tmp