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getgrouplist(3) [netbsd man page]

GETGROUPLIST(3) 					   BSD Library Functions Manual 					   GETGROUPLIST(3)

getgrouplist, getgroupmembership, -- calculate group access list LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> int getgrouplist(const char *name, gid_t basegid, gid_t *groups, int *ngroups); int getgroupmembership(const char *name, gid_t basegid, gid_t *groups, int maxgrp, int *ngroups); DESCRIPTION
The getgrouplist() and getgroupmembership() functions read through the group database and calculate the group access list for the user speci- fied in name. The basegid is automatically included in the groups list. Typically this value is given as the group number from the password database. The resulting group list is returned in the integer array pointed to by groups. For getgrouplist(), the caller specifies the size of the groups array in the integer pointed to by ngroups. For getgroupmembership(), the caller specifies the size of the groups array in maxgrp. The actual number of groups found is returned in ngroups. Duplicate group ids will be suppressed from the result. RETURN VALUES
The getgrouplist() and getgroupmembership() functions return 0 if successful, and return -1 if the size of the group list is too small to hold all the user's groups. In the latter case, the groups array will be filled with as many groups as will fit and ngroups will contain the total number of groups found. FILES
/etc/group group membership list SEE ALSO
setgroups(2), initgroups(3), group(5) HISTORY
The getgrouplist() function first appeared in 4.4BSD. The getgroupmembership() function first appeared in NetBSD 3.0 to address an API defi- ciency in getgrouplist(). BUGS
The getgrouplist() function uses the routines based on getgrent(3). If the invoking program uses any of these routines, the group structure will be overwritten in the call to getgrouplist(). BSD
January 6, 2005 BSD

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GETGROUPLIST(3) 					     Linux Programmer's Manual						   GETGROUPLIST(3)

getgrouplist - get list of groups to which a user belongs SYNOPSIS
#include <grp.h> int getgrouplist(const char *user, gid_t group, gid_t *groups, int *ngroups); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): getgrouplist(): _BSD_SOURCE DESCRIPTION
The getgrouplist() function scans the group database (see group(5)) to obtain the list of groups that user belongs to. Up to *ngroups of these groups are returned in the array groups. If it was not among the groups defined for user in the group database, then group is included in the list of groups returned by getgrou- plist(); typically this argument is specified as the group ID from the password record for user. The ngroups argument is a value-result argument: on return it always contains the number of groups found for user, including group; this value may be greater than the number of groups stored in groups. RETURN VALUE
If the number of groups of which user is a member is less than or equal to *ngroups, then the value *ngroups is returned. If the user is a member of more than *ngroups groups, then getgrouplist() returns -1. In this case the value returned in *ngroups can be used to resize the buffer passed to a further call getgrouplist(). VERSIONS
This function is present since glibc 2.2.4. CONFORMING TO
This function is nonstandard; it appears on most BSDs. BUGS
In glibc versions before 2.3.3, the implementation of this function contains a buffer-overrun bug: it returns the complete list of groups for user in the array groups, even when the number of groups exceeds *ngroups. EXAMPLE
The program below displays the group list for the user named in its first command-line argument. The second command-line argument speci- fies the ngroups value to be supplied to getgrouplist(). The following shell session shows examples of the use of this program: $ ./a.out cecilia 0 getgrouplist() returned -1; ngroups = 3 $ ./a.out cecilia 3 ngroups = 3 16 (dialout) 33 (video) 100 (users) Program source #include <stdio.h> #include <stdlib.h> #include <grp.h> #include <pwd.h> int main(int argc, char *argv[]) { int j, ngroups; gid_t *groups; struct passwd *pw; struct group *gr; if (argc != 3) { fprintf(stderr, "Usage: %s <user> <ngroups> ", argv[0]); exit(EXIT_FAILURE); } ngroups = atoi(argv[2]); groups = malloc(ngroups * sizeof (gid_t)); if (groups == NULL) { perror("malloc"); exit(EXIT_FAILURE); } /* Fetch passwd structure (contains first group ID for user) */ pw = getpwnam(argv[1]); if (pw == NULL) { perror("getpwnam"); exit(EXIT_SUCCESS); } /* Retrieve group list */ if (getgrouplist(argv[1], pw->pw_gid, groups, &ngroups) == -1) { fprintf(stderr, "getgrouplist() returned -1; ngroups = %d ", ngroups); exit(EXIT_FAILURE); } /* Display list of retrieved groups, along with group names */ fprintf(stderr, "ngroups = %d ", ngroups); for (j = 0; j < ngroups; j++) { printf("%d", groups[j]); gr = getgrgid(groups[j]); if (gr != NULL) printf(" (%s)", gr->gr_name); printf(" "); } exit(EXIT_SUCCESS); } SEE ALSO
getgroups(2), setgroups(2), getgrent(3), group(5), passwd(5) COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at GNU
2008-07-03 GETGROUPLIST(3)
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