Linux, Ubuntu, INotify - flash and pulseaudio sound stutter

This post was initially drafted on March 6.

Having issues with Linux slowing to a crawl over time? I certainly seemed to have this problem when running Ubuntu 12.10 and KDE (Kubuntu 12.10).

Initial symptom: Audio stutter using flash (e.g: YouTube)

Recently I had problems with Shockwave Flash misbehaving (frozen, stuttered video) in Chrome so I used the task manager (shift-escape, or right click in the tabs area) to kill the plugin and GPU processes. Unfortunately, reloading flash didn't fix the stutter, so I took a step further and killed pulseaudio. Pulseaudio manages access to the audio hardware and because has caused weird effects on my system's performance in the past it was next on the list.

pulseaudio refuses to start

However, trying to restart pulseaudio by typing 'pulseaudio' on the command line kept giving me this error:

E: [pulseaudio] module-udev-detect.c: inotify_init1() failed: Too many open files
E: [pulseaudio] module.c: Failed to load module "module-udev-detect" (argument: ""): initialization failed.
E: [pulseaudio] main.c: Module load failed.
E: [pulseaudio] main.c: Failed to initialize daemon.

Debugging the error

"Too many open files" is one of those generic and woefully overloaded errors that tends to provide little help in figuring out what's really happening. I checked my file descriptor limits using "ulimit -a" but the number of open files used by chrome was under this limit. In retrospect, this is not helpful information because 'ulimit' is used to set a limit on the number of file descriptors that can be opened by subsequent commands; it does not tell you how many files are currently open whether globally or in that shell. But running "pulseaudio -vvv" didn't provide much more useful detail:

shell$ ulimit -a[...]open files                (-n) 1024

The next tool in the toolbox is 'strace' - running "strace -fff pulseaudio" shows the error at the point that the system call being made:

inotify_init1(O_NONBLOCK|O_CLOEXEC)     = -1 EMFILE (Too many open files)

I checked the manpage for inotify_init1 which describes the error EMFILE as: "The user limit on the total number of inotify instances has been reached". By combining that with some additional searching, it appears that the system limit may be set too low for the number of inotify user instances. I found that my kernel defaults to 128:

shell$ cat /proc/sys/fs/inotify/max_user_instances 

128

Finding and fixing the root cause

And thanks to a pointer from https://github.com/nex3/rb-inotify/issues/23 to here:
http://unix.stackexchange.com/questions/13751/kernel-inotify-watch-limit-reached I updated this limit permanently:

root# sysctl -w  fs.inotify.max_user_instances=512 

fs.inotify.max_user_instances = 512 

root# grep inotify /etc/sysctl.conf 

root# vi /etc/sysctl.conf

Once I knew what I was looking for, this was easier to find:

http://askubuntu.com/questions/154255/how-can-i-tell-if-i-am-out-of-inotify-watches