chmod 700: private to the owner, the mode for ~/.ssh

What chmod 700 means

In 700 the first digit is the owner, the second the group and the third everyone else: the owner gets read, write and execute, the group gets no access at all, and others get no access at all.

ls -l shows -rwx------. On a directory, the two zeros mean other users cannot list it or traverse it, which also hides every file inside, whatever those files' own modes say.

The ~/.ssh case

OpenSSH checks permissions before trusting your keys. With the server's default StrictModes yes, sshd refuses public-key login if your home directory, ~/.ssh or authorized_keys is writable by group or others. The conventional fix is chmod 700 ~/.ssh and chmod 600 ~/.ssh/authorized_keys ~/.ssh/id_*, leaving the .pub files at 644 if you like.

The same reasoning applies to ~/.gnupg, which GnuPG warns about when it is accessible to others, and to any directory holding credentials or tokens.

Other uses and limits

700 is right for a personal script that reads secrets, and for scratch or build directories a single service account owns. Root is not restricted by these bits: an administrator, or anything running as root, can still read the contents. File modes protect users from each other, not from the machine's owner.

Do not apply 700 recursively to files that are only data; they gain an execute bit they do not need. Give directories 700 and files 600 with a find -type d / find -type f split, or chmod -R u=rwX,go= dir.

Related values

700 is the most private directory mode in this set. 750 opens it to one group, read and traverse only, which is the usual next step when a service must read the contents. 755 opens it to every account. For the files inside, 600 is the matching private mode, and 640 the group-readable one. If you find a private directory at 777, treat its contents as exposed and rotate any secrets in it.