#include <unistd.h>

int getgroups(int gidsetsize, gid_t grouplist[]);


Declared, not implemented


IEEE Std 1003.1-2017


The getgroups() function shall fill in the array grouplist with the current supplementary group IDs of the calling process. It is implementation-defined whether getgroups() also returns the effective group ID in the grouplist array.

The gidsetsize argument specifies the number of elements in the array grouplist. The actual number of group IDs stored in the array shall be returned. The values of array entries with indices greater than or equal to the value returned are undefined.

If gidsetsize is 0, getgroups() shall return the number of group IDs that it would otherwise return without modifying the array pointed to by grouplist.

If the effective group ID of the process is returned with the supplementary group IDs, the value returned shall always be greater than or equal to one and less than or equal to the value of NGROUPS_MAX+1.

Return value

Upon successful completion, the number of supplementary group IDs shall be returned. A return value of -1 indicates failure and errno shall be set to indicate the error.


The getgroups() function shall fail if:

  • EINVAL - The gidsetsize argument is non-zero and less than the number of group IDs that would have been returned.



Known bugs


See Also

  1. Standard library functions
  2. Table of Contents