setgroups(2)


NAME

   getgroups, setgroups - get/set list of supplementary group IDs

SYNOPSIS

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

   int getgroups(int size, gid_t list[]);

   #include <grp.h>

   int setgroups(size_t size, const gid_t *list);

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

   setgroups():
       Since glibc 2.19:
           _DEFAULT_SOURCE
       Glibc 2.19 and earlier:
           _BSD_SOURCE

DESCRIPTION

   getgroups()  returns the supplementary group IDs of the calling process
   in list.  The argument size should be set  to  the  maximum  number  of
   items  that  can  be  stored  in the buffer pointed to by list.  If the
   calling process is a member of more  than  size  supplementary  groups,
   then  an  error results.  It is unspecified whether the effective group
   ID of the calling process is included in the returned list.  (Thus,  an
   application should also call getegid(2) and add or remove the resulting
   value.)

   If size is zero,  list  is  not  modified,  but  the  total  number  of
   supplementary  group  IDs for the process is returned.  This allows the
   caller to determine the size of a dynamically allocated list to be used
   in a further call to getgroups().

   setgroups()  sets  the supplementary group IDs for the calling process.
   Appropriate privileges are required (see the description of  the  EPERM
   error, below).  The size argument specifies the number of supplementary
   group IDs in the buffer pointed to by list.

RETURN VALUE

   On success, getgroups() returns the number of supplementary group  IDs.
   On error, -1 is returned, and errno is set appropriately.

   On success, setgroups() returns 0.  On error, -1 is returned, and errno
   is set appropriately.

ERRORS

   EFAULT list has an invalid address.

   getgroups() can additionally fail with the following error:

   EINVAL size is less than the number of supplementary group IDs, but  is
          not zero.

   setgroups() can additionally fail with the following errors:

   EINVAL size  is  greater than NGROUPS_MAX (32 before Linux 2.6.4; 65536
          since Linux 2.6.4).

   ENOMEM Out of memory.

   EPERM  The calling process has insufficient privilege (the caller  does
          not  have  the  CAP_SETGID  capability  in the user namespace in
          which it resides).

   EPERM (since Linux 3.19)
          The use of setgroups() is denied in this  user  namespace.   See
          the description of /proc/[pid]/setgroups in user_namespaces(7).

CONFORMING TO

   SVr4,   4.3BSD.   The  getgroups()  function  is  in  POSIX.1-2001  and
   POSIX.1-2008.  Since setgroups() requires privilege, it is not  covered
   by POSIX.1.

NOTES

   A  process  can  have  up  to  NGROUPS_MAX  supplementary  group IDs in
   addition to the  effective  group  ID.   The  constant  NGROUPS_MAX  is
   defined in <limits.h>.  The set of supplementary group IDs is inherited
   from the parent process, and preserved across an execve(2).

   The maximum number of supplementary group IDs can be found at run  time
   using sysconf(3):

       long ngroups_max;
       ngroups_max = sysconf(_SC_NGROUPS_MAX);

   The  maximum return value of getgroups() cannot be larger than one more
   than  this  value.   Since  Linux  2.6.4,   the   maximum   number   of
   supplementary  group  IDs  is also exposed via the Linux-specific read-
   only file, /proc/sys/kernel/ngroups_max.

   The original Linux getgroups() system call supported only 16-bit  group
   IDs.   Subsequently,  Linux  2.4 added getgroups32(), supporting 32-bit
   IDs.  The glibc getgroups() wrapper function transparently  deals  with
   the variation across kernel versions.

   C library/kernel differences
   At the kernel level, user IDs and group IDs are a per-thread attribute.
   However, POSIX requires that all threads in a process  share  the  same
   credentials.   The  NPTL  threading  implementation  handles  the POSIX
   requirements by providing wrapper  functions  for  the  various  system
   calls  that  change  process  UIDs  and  GIDs.  These wrapper functions
   (including the one for setgroups()) employ a signal-based technique  to
   ensure  that  when  one  thread  changes  credentials, all of the other
   threads in the process also change their credentials.  For details, see
   nptl(7).

SEE ALSO

   getgid(2),  setgid(2), getgrouplist(3), group_member(3), initgroups(3),
   capabilities(7), credentials(7)

COLOPHON

   This page is part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.





Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.





Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.


Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.





Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.


Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.





Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.


Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.