Add a user to the system *only if it doesn't exist*

Question

I've been running the useradd {user} command to add users to my system, though I plan on running this in an automated environment, and it might end up being run again, even though the user already exists.

Is there a way that I can run this only if the user doesn't already exist? The user doesn't have a home folder.

Answer 1

id -u somename returns a non-zero exit code when the user does not exist.

You can test it quite simply... (&>/dev/null just supresses the normal output/warning)

id -u somename &>/dev/null || useradd somename 

Answer 2

try this:

useradd {user} || echo "User already exists."

or even this:

useradd {user} || true

Answer 3

Unless you only have a small handful of systems, you are asking the wrong question. The answer is not to run useradd at all, but instead leave this work to a configuration management solution like puppet or chef. This will allow your user definitions to be centralized and prevent you from running for loops and using ssh with root users in order to configure your systems. You will always have systems in a known configuration state.

Documentation for puppet is available at http://docs.puppetlabs.com

As an example in puppet:

user { "bob" : 
  password   => "$1$yv3n066X$Vpb05Ac/fHTicNdT9T5vz1", # generated with `openssl passwd -1`
  ensure     => present,                              # ensure => absent to remove
  managehome => true,
}

Answer 4

useradd would not add the user again if it exists already, it intends to make sure the uid number and uid login are unique. If you are planning to run through a batch, make sure the uids being used are unique; useradd would complain for the problematic entries and you need to capture the errors/stderr to see which user accounts had problems getting into the account systems (/etc/passwd, group, shadow).