What chmod 700 means
The owner digit is 7, combining read (4), write (2), and execute (1). The group and other-user digits are both 0. For a directory, the result appears as drwx------; for a regular executable file, it appears as -rwx------. Only the owner can inspect, change, or use the item through normal Unix permission checks.
On a directory, read allows the owner to list names, write allows entries to be created or removed, and execute allows traversal into the directory. Removing all three bits from group and other users makes both the directory listing and the paths beneath it inaccessible to ordinary accounts, subject to privileged access and any additional ACLs.
Why the ~/.ssh directory commonly uses 700
The ~/.ssh directory can reveal host aliases, usernames, known hosts, and the filenames of private keys. Mode 700 prevents another local user from listing those names or traversing the directory. It also prevents group members from adding or replacing files in a location that the SSH client trusts.
OpenSSH checks more than the key file itself. A key may have a restrictive mode and still fail when its parent directory is writable or accessible in an unsafe way. If SSH reports that a directory or key is too open, follow the SSH permissions troubleshooting steps to check the directory, file, owner, and key being loaded.
Private scripts and application directories
A user-private bin directory or a script that only its owner should run can also use 700. The execute bit is required for the script to run directly, while the zero group and other digits keep unrelated accounts from reading its source or invoking it. This can be appropriate for maintenance utilities that contain internal paths or account-specific operations.
The owner must still be correct. Applying 700 to an item owned by root will not give an ordinary user access, and applying it to a service directory may lock the service out when the process runs under another account. Fix ownership or choose a controlled group before widening permissions simply to make a process work.
700 compared with 755 and 600
chmod 755 lets group members and other users read and traverse a directory. Mode 700 removes that access completely, which makes it suitable for a private home subdirectory but unsuitable for a public web directory that a server or other users must traverse.
Private files more commonly use chmod 600 because ordinary data and private keys do not need execute permission. Use 700 when the owner must traverse a directory or run a file; use 600 when the owner only needs to read and write a non-executable file.