Skip to main content

Too many open files? Increasing the limit in C.

I ran into error 24 today: "Too many open files". Ooops. The solution that I eventually went for is not among the first Google hits for "increase limit open files" so I felt like blogging about it here. There are two functions getrlimit and setrlimit that allow querying and modifying certain resource limits, e.g. the maximum number of open files for a single process (and they do have a shared, detailed man page). For each of the resource limit types, there is a hard and a soft limit: the soft limit, is the one you run into. In my case the soft is 1024, the hard one is 4096. The cool things is: Any non-root process can increase the soft limit to the hard one. That's my rescue. Simplified, this is what I do:

#include <sys/time.h>
#include <sys/resource.h>


struct rlimit open_file_limit;

/* Query current soft/hard value */
getrlimit(RLIMIT_NOFILE, &open;_file_limit);

/* Set soft limit to hard limit */
open_file_limit.rlim_cur = open_file_limit.rlim_max;
setrlimit(RLIMIT_NOFILE, &open;_file_limit);

Works like a charm.