System vs Regular Users
Linux users can be "system" users or "normal" users.
- Regular users typically have UID's at 1000 or higher and are allowed to log into the server.
- System users often have a user id (UID) below 1000 and cannot be used to login. They are usually used to run programs. For example, users www-data or apache are often used to run web servers.
See the file /etc/login.defs to find variables like UID_MIN and UID_MAX set for system vs regular users:
# # Min/max values for automatic uid selection in useradd # UID_MIN 1000 UID_MAX 60000 # System accounts SYS_UID_MIN 201 SYS_UID_MAX 999 # # Min/max values for automatic gid selection in groupadd # GID_MIN 1000 GID_MAX 60000 # System accounts SYS_GID_MIN 201 SYS_GID_MAX 999