1GETGROUPS(2)               Linux Programmer's Manual              GETGROUPS(2)
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NAME

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

9       #include <sys/types.h>
10       #include <unistd.h>
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12       int getgroups(int size, gid_t list[]);
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14       #include <grp.h>
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16       int setgroups(size_t size, const gid_t *list);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       setgroups():
21           Since glibc 2.19:
22               _DEFAULT_SOURCE
23           Glibc 2.19 and earlier:
24               _BSD_SOURCE
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DESCRIPTION

27       getgroups()  returns the supplementary group IDs of the calling process
28       in list.  The argument size should be set  to  the  maximum  number  of
29       items  that  can  be  stored  in the buffer pointed to by list.  If the
30       calling process is a member of more  than  size  supplementary  groups,
31       then  an  error results.  It is unspecified whether the effective group
32       ID of the calling process is included in the returned list.  (Thus,  an
33       application should also call getegid(2) and add or remove the resulting
34       value.)
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36       If size is zero, list is not modified, but the total number of  supple‐
37       mentary  group IDs for the process is returned.  This allows the caller
38       to determine the size of a dynamically allocated list to be used  in  a
39       further call to getgroups().
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41       setgroups()  sets  the supplementary group IDs for the calling process.
42       Appropriate privileges are required (see the description of  the  EPERM
43       error, below).  The size argument specifies the number of supplementary
44       group IDs in the buffer pointed to by list.
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RETURN VALUE

47       On success, getgroups() returns the number of supplementary group  IDs.
48       On error, -1 is returned, and errno is set appropriately.
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50       On success, setgroups() returns 0.  On error, -1 is returned, and errno
51       is set appropriately.
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ERRORS

54       EFAULT list has an invalid address.
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56       getgroups() can additionally fail with the following error:
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58       EINVAL size is less than the number of supplementary group IDs, but  is
59              not zero.
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61       setgroups() can additionally fail with the following errors:
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63       EINVAL size  is  greater than NGROUPS_MAX (32 before Linux 2.6.4; 65536
64              since Linux 2.6.4).
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66       ENOMEM Out of memory.
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68       EPERM  The calling process has insufficient privilege (the caller  does
69              not  have  the  CAP_SETGID  capability  in the user namespace in
70              which it resides).
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72       EPERM (since Linux 3.19)
73              The use of setgroups() is denied in this  user  namespace.   See
74              the description of /proc/[pid]/setgroups in user_namespaces(7).
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CONFORMING TO

77       getgroups(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
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79       setgroups(): SVr4, 4.3BSD.  Since setgroups() requires privilege, it is
80       not covered by POSIX.1.
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NOTES

83       A