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Diffstat (limited to 'man/man3/getgrouplist.3')
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diff --git a/man/man3/getgrouplist.3 b/man/man3/getgrouplist.3 new file mode 100644 index 0000000..4a8f5fb --- /dev/null +++ b/man/man3/getgrouplist.3 @@ -0,0 +1,205 @@ +'\" t +.\" Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk +.\" <mtk.manpages@gmail.com> +.\" +.\" A few pieces remain from an earlier version written in +.\" 2002 by Walter Harms (walter.harms@informatik.uni-oldenburg.de) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH getgrouplist 3 2024-05-02 "Linux man-pages (unreleased)" +.SH NAME +getgrouplist \- get list of groups to which a user belongs +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <grp.h> +.P +.BI "int getgrouplist(const char *" user ", gid_t " group , +.BI " gid_t *" groups ", int *" ngroups ); +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.BR getgrouplist (): +.nf + Since glibc 2.19: + _DEFAULT_SOURCE + glibc 2.19 and earlier: + _BSD_SOURCE +.fi +.SH DESCRIPTION +The +.BR getgrouplist () +function scans the group database (see +.BR group (5)) +to obtain the list of groups that +.I user +belongs to. +Up to +.I *ngroups +of these groups are returned in the array +.IR groups . +.P +If it was not among the groups defined for +.I user +in the group database, then +.I group +is included in the list of groups returned by +.BR getgrouplist (); +typically this argument is specified as the group ID from +the password record for +.IR user . +.P +The +.I ngroups +argument is a value-result argument: +on return it always contains the number of groups found for +.IR user , +including +.IR group ; +this value may be greater than the number of groups stored in +.IR groups . +.SH RETURN VALUE +If the number of groups of which +.I user +is a member is less than or equal to +.IR *ngroups , +then the value +.I *ngroups +is returned. +.P +If the user is a member of more than +.I *ngroups +groups, then +.BR getgrouplist () +returns \-1. +In this case, the value returned in +.I *ngroups +can be used to resize the buffer passed to a further call to +.BR getgrouplist (). +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR getgrouplist () +T} Thread safety MT-Safe locale +.TE +.SH STANDARDS +None. +.SH HISTORY +glibc 2.2.4. +.SH BUGS +Before glibc 2.3.3, +the implementation of this function contains a buffer-overrun bug: +it returns the complete list of groups for +.I user +in the array +.IR groups , +even when the number of groups exceeds +.IR *ngroups . +.SH EXAMPLES +The program below displays the group list for the user named in its +first command-line argument. +The second command-line argument specifies the +.I ngroups +value to be supplied to +.BR getgrouplist (). +The following shell session shows examples of the use of this program: +.P +.in +4n +.EX +.RB "$" " ./a.out cecilia 0" +getgrouplist() returned \-1; ngroups = 3 +.RB "$" " ./a.out cecilia 3" +ngroups = 3 +16 (dialout) +33 (video) +100 (users) +.EE +.in +.SS Program source +\& +.\" SRC BEGIN (getgrouplist.c) +.EX +#include <errno.h> +#include <grp.h> +#include <pwd.h> +#include <stdio.h> +#include <stdlib.h> +\& +int +main(int argc, char *argv[]) +{ + int ngroups; + gid_t *groups; + struct group *gr; + struct passwd *pw; +\& + if (argc != 3) { + fprintf(stderr, "Usage: %s <user> <ngroups>\en", argv[0]); + exit(EXIT_FAILURE); + } +\& + ngroups = atoi(argv[2]); +\& + groups = malloc(sizeof(*groups) * ngroups); + if (groups == NULL) { + perror("malloc"); + exit(EXIT_FAILURE); + } +\& + /* Fetch passwd structure (contains first group ID for user). */ +\& + errno = 0; + pw = getpwnam(argv[1]); + if (pw == NULL) { + if (errno) + perror("getpwnam"); + else + fprintf(stderr, "no such user\en"); + exit(EXIT_FAILURE); + } +\& + /* Retrieve group list. */ +\& + if (getgrouplist(argv[1], pw\->pw_gid, groups, &ngroups) == \-1) { + fprintf(stderr, "getgrouplist() returned \-1; ngroups = %d\en", + ngroups); + exit(EXIT_FAILURE); + } +\& + /* Display list of retrieved groups, along with group names. */ +\& + fprintf(stderr, "ngroups = %d\en", ngroups); + for (int j = 0; j < ngroups; j++) { + printf("%d", groups[j]); + gr = getgrgid(groups[j]); + if (gr != NULL) + printf(" (%s)", gr\->gr_name); + printf("\en"); + } +\& + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR getgroups (2), +.BR setgroups (2), +.BR getgrent (3), +.BR group_member (3), +.BR group (5), +.BR passwd (5) |