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SETGROUPS(2) System Calls Manual SETGROUPS(2)

set group access list

#include <sys/types.h>
#include <unistd.h>
setgroups(int ngroups, const gid_t *gidset);

setgroups() sets the group access list of the current user process according to the array gidset. The parameter ngroups indicates the number of entries in the array and must be no more than {NGROUPS_MAX}.
Only the superuser may set new groups.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The setgroups() call will fail if:
The value of ngroups is greater than {NGROUPS_MAX}.
The caller is not the superuser.
The address specified for gidset is outside the process address space.

getgroups(2), setgid(2), setregid(2), initgroups(3)

The setgroups() system call first appeared in 4.1cBSD.
September 10, 2015 OpenBSD-current