1GETGRGID(3P) POSIX Programmer's Manual GETGRGID(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 getgrgid, getgrgid_r — get group database entry for a group ID
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15 #include <grp.h>
16 struct group *getgrgid(gid_t gid);
18 int getgrgid_r(gid_t gid, struct group *grp, char *buffer,
19 size_t bufsize, struct group **result);
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22 The getgrgid() function shall search the group database for an entry
23 with a matching gid.
24 The getgrgid() function need not be thread-safe.
26 Applications wishing to check for error situations should set errno to
28 0 before calling getgrgid(). If getgrgid() returns a null pointer and
29 errno is set to non-zero, an error occurred.
30 The getgrgid_r() function shall update the group structure pointed to
32 by grp and store a pointer to that structure at the location pointed to
33 by result. The structure shall contain an entry from the group data‐
34 base with a matching gid. Storage referenced by the group structure is
35 allocated from the memory provided with the buffer parameter, which is
36 bufsize bytes in size. A call to sysconf(_SC_GETGR_R_SIZE_MAX) returns
37 either -1 without changing errno or an initial value suggested for the
38 size of this buffer. A null pointer shall be returned at the location
39 pointed to by result on error or if the requested entry is not found.
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42 Upon successful completion, getgrgid() shall return a pointer to a
43 struct group with the structure defined in <grp.h> with a matching
44 entry if one is found. The getgrgid() function shall return a null
45 pointer if either the requested entry was not found, or an error
46 occurred. If the requested entry was not found, errno shall not be
47 changed. On error, errno shall be set to indicate the error.
48 The application shall not modify the structure to which the return
50 value points, nor any storage areas pointed to by pointers within the
51 structure. The returned pointer, and pointers within the structure,
52 might be invalidated or the structure or the storage areas might be
53 overwritten by a subsequent call to getgrent(), getgrgid(), or getgr‐
54 nam(). The returned pointer, and pointers within the structure, might
55 also be invalidated if the calling thread is terminated.
56 If successful, the getgrgid_r() function shall return zero; otherwise,
58 an error number shall be returned to indicate the error.
59
61 The getgrgid() and getgrgid_r() functions may fail if:
62 EIO An I/O error has occurred.
64 EINTR A signal was caught during getgrgid().
66 EMFILE All file descriptors available to the process are currently
68 open.
69 ENFILE The maximum allowable number of files is currently open in the
71 system.
72 The getgrgid_r() function may fail if:
74 ERANGE Insufficient storage was supplied via buffer and bufsize to con‐
76 tain the data to be referenced by the resulting group structure.
77 The following sections are informative.
79
81 Note that sysconf(_SC_GETGR_R_SIZE_MAX) may return -1 if there is no
82 hard limit on the size of the buffer needed to store all the groups
83 returned. This example shows how an application can allocate a buffer
84 of sufficient size to work with getgrid_r().
85 long int initlen = sysconf(_SC_GETGR_R_SIZE_MAX);
88 size_t len;
89 if (initlen == -1)
90 /* Default initial length. */
91 len = 1024;
92 else
93 len = (size_t) initlen;
94 struct group result;
95 struct group *resultp;
96 char *buffer = malloc(len);
97 if (buffer == NULL)
98 ...handle error...
99 int e;
100 while ((e = getgrgid_r(42, &result, buffer, len, &resultp)) == ERANGE)
101 {
102 size_t newlen = 2 * len;
103 if (newlen < len)
104 ...handle error...
105 len = newlen;
106 char *newbuffer = realloc(buffer, len);
107 if (newbuffer == NULL)
108 ...handle error...
109 buffer = newbuffer;
110 }
111 if (e != 0)
112 ...handle error...
113 free (buffer);
114 Finding an Entry in the Group Database
116 The following example uses getgrgid() to search the group database for
117 a group ID that was previously stored in a stat structure, then prints
118 out the group name if it is found. If the group is not found, the pro‐
119 gram prints the numeric value of the group for the entry.
120 #include <sys/types.h>
123 #include <grp.h>
124 #include <stdio.h>
125 ...
126 struct stat statbuf;
127 struct group *grp;
128 ...
129 if ((grp = getgrgid(statbuf.st_gid)) != NULL)
130 printf(" %-8.8s", grp->gr_name);
131 else
132 printf(" %-8d", statbuf.st_gid);
133 ...
134
136 The getgrgid_r() function is thread-safe and shall return values in a
137 user-supplied buffer instead of possibly using a static data area that
138 may be overwritten by each call.
139 Portable applications should take into account that it is usual for an
141 implementation to return -1 from sysconf() indicating that there is no
142 maximum for _SC_GETGR_R_SIZE_MAX.
143
145 None.
146
148 None.
149
151 endgrent(), getgrnam(), sysconf()
152 The Base Definitions volume of POSIX.1‐2017, <grp.h>, <sys_types.h>
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156 Portions of this text are reprinted and reproduced in electronic form
157 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
158 table Operating System Interface (POSIX), The Open Group Base Specifi‐
159 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
160 Electrical and Electronics Engineers, Inc and The Open Group. In the
161 event of any discrepancy between this version and the original IEEE and
162 The Open Group Standard, the original IEEE and The Open Group Standard
163 is the referee document. The original Standard can be obtained online
164 at http://www.opengroup.org/unix/online.html .
165 Any typographical or formatting errors that appear in this page are
167 most likely to have been introduced during the conversion of the source
168 files to man page format. To report such errors, see https://www.ker‐
169 nel.org/doc/man-pages/reporting_bugs.html .
170IEEE/The Open Group 2017 GETGRGID(3P)