Unix permissions control who can access and modify files and directories. To check the permissions of a file or directory, use the `ls -l` command. This command will list all of the files and directories in the current directory, along with their permissions.
The permissions are divided into three groups: user, group, and other. Each group has three permissions: read, write, and execute. The user group is the owner of the file or directory. The group group is the group that the file or directory belongs to. The other group is everyone else.
