Debugging open file handles in emacs

Question

Is there a way I can find what file handles emacs has open, and close these references? Or even better, find where they are being open?

Emacs is keeping handles to a large number of files (a leak) that I don't have corresponding buffers to. My standard method of closing a buffer has been using the kill-buffer command.

Context:

I am having a reoccurring issue, where after a day or two of being open I can no longer do any file operations in emacs, due to a "Too many open files" error when creating a pipe. I am on OSX 10.10.4, Emacs 25.0.50 installed with homebrew.

Here is a sample of emacs' open files according to Activity Monitor (double click on emacs and select "Open Files and Ports").

/Users/Ash/Dropbox/org
/Users/Ash/Dropbox/org
/Users/Ash/Dropbox/org
/Users/Ash/Dropbox/org
/Users/Ash/Documents/workspace/roboclub/Federation-Place
/Users/Ash/Documents/workspace/roboclub/Federation-Place
/Users/Ash/Documents/workspace/roboclub/Federation-Place
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript/status
/Users/Ash/Dropbox/org
/Users/Ash/Dropbox/org
/Users/Ash/Dropbox/org
/Users/Ash/Dropbox/org
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript/status
/Users/Ash/Documents/workspace/roboclub/Federation-Place
/Users/Ash/Documents/workspace/roboclub/Federation-Place
/Users/Ash/Documents/workspace/roboclub/Federation-Place
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript/status
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript/status
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript/status
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript/status
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript
/Users/Ash/Documents/workspace/roboclub/Federation-Place/web/site/src/javascript

There are actually many more files open, but you can see that they are being repeated. (Also these are folders, not sure why that is).

Update

The following are my file limits:

$ ulimit -n
4096
$ sysctl -a | grep files
kern.maxfiles: 20480
kern.maxfilesperproc: 10240
kern.num_files: 4496

And my open files:

$ lsof | awk '{print $1 "-" $2}' | sort | uniq -c | sort -nr | head -10
 728 Google-345
 508 Google-551
 430 Mail-353
 418 Skype-12098
 356 Dock-361
 350 Emacs-8847
 207 Dropbox-637
 176 Google-22455
 176 Google-21229
 165 Google-26072

Emacs is the only program having issues, yet doesn't seem to have a comparatively high file count.

Answer 1

This error is probably related to OS restrictions on max open files and unrelated to Emacs. You can check what processes are running under Emacs with this command:

M-x list-processes

The most common tool to see which file is opened by which process/program, use lsof tool at the system command prompt (outside Emacs):

lsof +f

the +f shows only filesystem entries (files and directories) and not all network pipes too. In any case, to fix the max open files, you will have to play with a few settings. Start with

sysctl -A | grep maxfiles

and increase the values for

kern.maxfiles = 12288
kern.maxfilesperproc = 10240

by editing (as sudo) this file

/etc/launchd.conf

and this line with suitable values (instead of 64K shown below)

limit maxfiles 65536 65536

then reboot OS X (logging off alone won't be enough for launchd settings). Fine tuning the max capacities is an art and is greatly dependent on what all things your installed programs are doing on your machine on your behalf!

OS X has a manpage for sysctl with lots more details.