What does chmod 700 mean? Private folder permissions explained

In octal, the owner's digit is 7, made from 4 + 2 + 1. The chmod(1) manual says a numeric mode comes from adding up the bit values. The group and others digits, 0 and 0, add up to nothing, so neither can read, write or enter.

On a folder, execute is the bit that lets you in, and read only lets you list the names. That's why 700 is the folder version of chmod 600. A folder at 600 gives the owner read and write but no execute, so the names can be listed while the files inside stay out of reach.

The ssh(1) manual says the recommended permissions for ~/.ssh/ are 'read/write/execute for the user, and not accessible by others.' A file can have 700 too. The owner then gets execute, so a script with a first line like #!/bin/bash can run as ./backup.sh, and only the owner can run it.

Keep 700 for folders like ~/.ssh or a folder of personal notes, where no other account has any reason to look inside. For a private file that doesn't need to run, use 600 or 400 instead.

Don't use 700 when a web server or another account has to read the folder. Those accounts need read and enter, so chmod 755 fits, or 750 when they share a group with you. For a shared project folder, a group mode works better than 700.

Watch out for chmod -R 700 dir. The -R flag applies the mode to every file inside, so every file gets execute for the owner. Set the files to 600 instead with find ~/private -type f -exec chmod 600 {} +. The -type f part picks regular files only, so folders are left alone.