chmod 400

Unix file permission mode 400 explained in detail.

Symbolic Notation

-r--------(as shown by ls -l)

-r--------

typeownergroupother

Permission Matrix

	Read(4)	Write(2)	Execute(1)	Octal
Owner	r	-	-	4
Group	-	-	-	0
Other	-	-	-	0

What Does chmod 400 Mean?

Owner can read. Group can no access. Others can no access.

$ chmod 400 filename

Common Use Cases

Read-only for the owner. Common for sensitive private keys and certificates (e.g., SSL certs).

Security Notes

Good for secrets. SSH enforces this — it will refuse a private key with overly permissive modes.

Other Common Modes

Interactive Tool

Need to calculate a custom permission? Use the interactive permissions calculator to toggle individual bits and get instant results.