What chmod 600 grants
The first digit is 6, combining read (4) and write (2) for the owner. The group and other-user digits are 0, so those classes receive no permissions. The symbolic result is rw-------. The owner can view and update the file, but the file is not executable and no other ordinary account can read it through standard Unix permission checks.
600 is a file mode. A directory usually needs execute permission so its owner can enter it, which is why a private directory commonly uses 700 instead. A file inside that directory may still use 600 for an additional layer of access control.
Why SSH private keys need 600
An SSH private key proves your identity to a remote server. If another local user can read that key, that user may be able to authenticate as you. OpenSSH therefore checks private-key permissions before use. When a key is accessible to group members or other users, ssh can refuse to load it and report that the permissions are too open.
Setting the private key to 600 satisfies the common requirement: the owner can read the key and replace it, while other users cannot. The key must also belong to the account running ssh. If chmod 600 does not solve the warning, inspect the owner with ls -l and correct ownership rather than adding broader permissions. Public keys are not secret and can usually be more readable; the restriction applies to the private key.
Dotfiles, tokens, and credential files
600 is also useful for files such as .env, cloud credentials, API tokens, password-store exports, database client settings, and private backups. These files often need to be edited by one account but never read by unrelated users. Owner-only access reduces accidental disclosure on shared workstations, development servers, and multi-user Linux hosts.
The application reading the file must run as the owner or with an explicitly designed privilege path. If a web service cannot read a 600 file, changing it to world-readable is usually the wrong response. Assign the correct owner, use a controlled service group with a carefully chosen mode, or move the secret into the platform's supported secret store.
600 compared with 644
chmod 644 keeps owner write access but lets every user read the file. That is suitable for public web assets and non-secret configuration, not private credentials. chmod 755 goes further by adding execute permission and is intended for traversable directories or executable files, not keys.
Remember that permissions are not encryption. Root, privileged backup software, or a compromised owner account may still read the file. Verify ownership, protect backups, and rotate exposed credentials. Use the chmod calculator to compare 600 with another mode before granting additional group or other-user access.