User IDs

Process data and Ownership data in Linux use UIDs exclusively.

This can create diffculties if a user is deleted while he still owns files in the filesystem. His UID can perhaps be assigned to a different user, and that user will inherit the previous UID owners files.

There is no technical problem with assigning the same numerical UID to different usernames but these users will have equal access to the files owned by that numeric UID. Don’t do it if you don’t have to.

We can find out an account id with


id for users root and grumpyolme on a debian system Screenshot 2015-12-18 14.29.09.png

id for user aamnah on a Mac OS X system Screenshot 2015-12-18 14.28.31.png

id will give you the

  • user id id -u username
  • group id id -g username
  • other groups the user is a member of id -G username. similar to groups username

root’s UID is always 0. that’s how you determine if the user is root in bash scripts..