I did some more digging and it looks like Mac OS X (BASH? BASH on Mac OS X? BSD? POSIX?) limits the number of files that a program can have open. Increasing this limit makes the issue disappear. By default, user accounts are limited to 256 open files (per process?) but this can be changed with ulimit. To see the current limit, type in `ulimit -n'. To increase the allowed number of files to the maximum, type in `ulimit -n unlimited'. Sometimes an error message will be generated, sometimes not. If a message is generated, restart Terminal.app and try again. After the operation succeeds, it's probably a good idea to set the limit back to its original value (`ulimit -n 256'). After doing some testing, it appears that 256 files is only slightly too small; `darcs pull -a' succeeds (at the moment) when the file limit is set to 320. I'll update the GHC wiki and follow up on the darcs bug in a bit. Richard