12/12/94
 
  Changing Group Membership from a Shell Script
 
 
 
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       knowledge at the time of this writing.  Please send feedback
       by fax to "AIXServ Information" at (512) 823-4009.
 
       Please use this information with care.  IBM will not be
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       operational environment.
 
  ABOUT THIS DOCUMENT
 
       This document describes a method of using a non-interactive
       script to change group membership and bypass group limits.
       This document applies to AIX 3.1, 3.2, and 4.1.
 
  INTRODUCTION
 
       AIX includes two commands for changing group set membership.
       They are "newgrp" and "setgroups".  Both of these commands
       require that the user enter the command from the command
       line, because these commands cannot be executed from a shell
       script.
 
       The sample code in this document provides a way to set the
       real and effective group ID from a shell script.  The tool
       verifies that the current user is a member of the target
       group before executing the named command.
 
  SAMPLE CODE
 
       NOTE:  Please note that page headers and footers may appear
       in the following code.  They should be removed before the
       code is used.  Also, revision bars (vertical bars in the
       left margin which mark changes in the document) may appear
       to the left of the code and should be removed before the
       code is used.
 
 
  /*
   * NAME: switchgrp
   *
   * COMPILATION:
   *   cc -o switchgrp switchgrp.c
   *   chown root switchgrp
   *   chmod 4555 switchgrp
   *   mv switchgrp <local extensions directory>
   *
   * FUNCTION:
   *   Set real and effective group ID to a value from /etc/group.
   *
   * DESCRIPTION:
   *   switchgrp allows a user to bypass the 32-group limitation without
 
                        Changing Group Membership from a Shell Script  1
 
 
                                                                12/12/94
 
   *   using the newgrp command.  newgrp cannot be used inside a shell
   *   script because of how it works.
   */
 
  #include <stdio.h>
  #include <pwd.h>
  #include <grp.h>
  #include <sys/id.h>
 
  main (int argc, char ** argv)
  {
      char      *newgrp = argv[1];
      struct    passwd  *pwd;
      struct    group   *grp;
      int       i;
 
      if (argc < 3) {
          fprintf (stderr, "usage: switchgrp group cmd [ args ]\n");
          exit (1);
      }
      if (! (grp = getgrnam (newgrp))) {
          fprintf (stderr, "unknown group: %s\n", newgrp);
          exit (1);
      }
      if (! (pwd = getpwuid (getuid ()))) {
          fprintf (stderr, "who are you?\n");
          exit (1);
      }
      for (i = 0;grp->gr_mem[i];i++)
          if (strcmp (pwd->pw_name, grp->gr_mem[i]) == 0)
                  break;
 
      if (grp->gr_mem[i] == (char *) 0) {
          fprintf (stderr, "not a member\n");
          exit (1);
      }
      setgidx (ID_REAL|ID_EFFECTIVE, grp->gr_gid);
      setuid (getuid ());
 
      execvp (argv[2], &argv[2]);
      perror (argv[2]);
      exit (255);
  }
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
                        Changing Group Membership from a Shell Script  2
 
 
                                                                12/12/94
 
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  END OF DOCUMENT (setgrp.script.31-41.cmd)
 
 
 
                        Changing Group Membership from a Shell Script  3