getgroups usage on linux Post: 302518149

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Top Forums Programming getgroups usage on linux Post 302518149 by achenle on Thursday 28th of April 2011 05:48:09 PM

04-28-2011

Registered User

How about this:

Code:

#include <grp.h>
#include <string.h>

gid_t *getGroups( const char *username, int *count )
{
    struct group *grp;
    gid_t *list = NULL;
    *count = 0;

    setgrent();

    for ( ;; )
    {
        int ii;

        grp = getgrent();
        if ( NULL == grp )
        {
            break;
        }

        if ( ( NULL == grp->gr_mem ) ||
             ( NULL == grp->gr_mem[ 0 ] ) )
        {
            continue;
        }

        ii = 0;
        for ( ii = 0;
              NULL != grp->gr_mem[ ii ];
              ii++ )
        {
            if ( 0 == strcmp( grp->gr_mem[ ii ], username ) )
            {
                list = ( gid_t * ) realloc( list,
                    ( *count + 1 ) * sizeof( gid_t ) );
                if ( NULL == list )
                {
                    endgrent();
                    return( NULL );
                }

                list[ *count ] = grp->gr_gid;
                ( *count )++;
                break;
            }
        }
    }
    endgrent();

    return( list );
}

Not very efficient with all those realloc()'s, and it's not reentrant, but it works.

On Solaris, you can cheat and use this:

Cross Reference: /onnv/onnv-gate/usr/src/lib/libc/port/gen/getgrnam_r.c

achenle

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setgroups

getgroups(2)							   System Calls 						      getgroups(2)

NAME

       getgroups, setgroups - get or set supplementary group access list IDs

SYNOPSIS

       #include <unistd.h>

       int getgroups(int gidsetsize, gid_t *grouplist);

       int setgroups(int ngroups, const gid_t *grouplist);

DESCRIPTION

       The getgroups() function gets the current supplemental group access list of the calling process and stores the result in the array of group
       IDs specified by grouplist. This array has gidsetsize entries and must be large enough to contain the entire  list.  This  list	cannot	be
       larger than NGROUPS_UMAX. If gidsetsize equals 0, getgroups() will return the number of groups to which the calling process belongs without
       modifying the array pointed to by grouplist.

       The setgroups() function sets the supplementary group access list of the calling process from the array of group  IDs  specified  by  grou-
       plist. The number of entries is specified by ngroups and can not be greater than NGROUPS_MAX.

RETURN VALUES

       Upon  successful  completion, getgroups() returns the number of supplementary group IDs set for the calling process and setgroups() returns
       0. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       The getgroups() and setgroups() functions will fail if:

       EFAULT	 A referenced part of the array pointed to by grouplist is an illegal address.

       The getgroups() function will fail if:

       EINVAL	 The value of gidsetsize is non-zero and less than the number of supplementary group IDs set for the calling process.

       The setgroups() function will fail if:

       EINVAL	 The value of ngroups is greater than {NGROUPS_MAX}.

       EPERM	 The {PRIV_PROC_SETID} privilege is not asserted in the effective set of the calling process.

USAGE

       Use of the setgroups() function requires the {PRIV_PROC_SETID} privilege.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |getgroups() is Standard.	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       groups(1), chown(2), getuid(2), setuid(2), getgrnam(3C), initgroups(3C), attributes(5), privileges(5), standards(5)

SunOS 5.11							    8 Sep 2006							      getgroups(2)

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