Creating new daemon users on Leopard

Created 10/30/2007, updated 3/12/20242 minute read

I just made a curious realization while trying to build MySQL for Leopard: I don’t know how to create new daemon user. No doubt this is ridiculously easy with Mac OS X Server, but in the non-server version it’s far from obvious.

The NetInfo Manager utility has finally be laid to rest, but so have command line tools like adduser. The /etc/passwd file starts with this info:

##
# User Database
#
# Note that this file is consulted directly only when the system is running
# in single-user mode.  At other times this information is provided by
# Open Directory.
#
# This file will not be consulted for authentication unless the BSD local node
# is enabled via /Applications/Utilities/Directory Utility.app
#
# See the DirectoryService(8) man page for additional information about
# Open Directory.
##

So what am I supposed to do? Use the Directory Utility application to turn on the BSD local node and then manually edit /etc/passwd and set a password using the passwd tool (for which there is no longer a manpage, but at least password --foo causes usage information to be printed)? Is there a more elegant way than this? What does Mac OS X Server do under the hood?

Update

Luckily, thanks to somebody who didn’t know that Leopard was under an NDA, found this article published back in April describing the dscl tool, a command line interface for Directory Services.
http://docs.info.apple.com/article.html?artnum=306494
http://www.royhooper.ca/blog/articles/2007/10/27/creating-os-only-users-on-leopard

So it looks like something like this would probably work:

sudo dscl localhost -create /Local/Default/Users/_mysql
sudo dscl localhost -create /Local/Default/Users/_mysql NFSHomeDirectory /var/empty
sudo dscl localhost -create /Local/Default/Users/_mysql Password '*'
sudo dscl localhost -create /Local/Default/Users/_mysql PrimaryGroupID 74
sudo dscl localhost -create /Local/Default/Users/_mysql RealName "MySQL Server"
sudo dscl localhost -create /Local/Default/Users/_mysql UniqueID: 74
sudo dscl localhost -create /Local/Default/Users/_mysql UserShell: /usr/bin/false

But, having started to snoop around using dscl I saw that there already is a MySQL user, it’s just that it appears as _mysql. Information about it can be printed by issuing one of the following commands:

# with leading underscore
dscl localhost -cat /Local/Default/Users/_mysql

# without
dscl localhost -cat /Local/Default/Users/mysql

The output is:

AppleMetaNodeLocation: /Local/Default
NFSHomeDirectory: /var/empty
Password: *
PrimaryGroupID: 74
RealName:
 MySQL Server
RecordName: _mysql mysql
RecordType: dsRecTypeStandard:Users
UniqueID: 74
UserShell: /usr/bin/false

I have no way of knowing whether this user is created by default when installing Leopard or if this was migrated over automatically when I performed my archive install. (Update: Martin Maciaszek wrote in to say that he did a clean install and the _mysql user, along with others like _svn, is created during installation; he also notes that "almost all the user ids below 100 are taken now".)

The _mysql and mysql user names appear to be completely equivalent in use (ie. chown mysql foo is identical to chown _mysql foo).

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