-1 not a valid limit for nofile in limits.conf

[Michael Schurter]

The LIMITS.CONF(5) manual states:

  All items support the values -1, unlimited or infinity indicating no limit, except for priority and nice.

However, this line in limits.conf appears to have no affect:

  * - nofile -1

Whereas this line works as expected (sets ulimit -n to 100000):

  * - nofile 100000

Turning on debugging for pam_limits.so doesn't give any more indication that -1 is invalid for nofile:

  pam_limits(login:session): process_limit: processing - nofile -1 for DEFAULT

The same line is logged for valid limits:

  pam_limits(login:session): process_limit: processing - nofile 100000 for DEFAULT

The LIMITS.CONF(5) man page does stipulate:

  If a hard limit or soft limit of a resource is set to a valid value, but outside of the supported range of the local system, the system may reject the new limit or unexpected behavior may occur.

So it seems having pam_limits not apply isn't entirely undocumented, however it'd be nice if nofile & -1 were explicitly mentioned.