initgroups — initialize the supplementary group access list


#include <sys/types.h>
#include <grp.h>

int initgroups(const char *user, gid_t group);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   Since glibc 2.19:
   Glibc 2.19 and earlier:


The initgroups() function initializes the group access list by reading the group database /etc/group and using all groups of which user is a member. The additional group group is also added to the list.

The user argument must be non-NULL.

Return Value

The initgroups() function returns 0 on success. On error, -1 is returned, and errno is set appropriately.



Insufficient memory to allocate group information structure.


The calling process has insufficient privilege. See the underlying system call setgroups(2).



group database file


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
initgroups() Thread safety MT-Safe locale

Conforming to

SVr4, 4.3BSD.

See Also

getgroups(2), setgroups(2), credentials(7)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

credentials(7), getgroups(2), group(5), nss(5), setpriv(1), slapd(8).

2017-09-15 GNU Linux Programmer's Manual