This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
getgrnam, getgrnam_r — search group database for a name
struct group *getgrnam(const char * name);
int getgrnam_r(const char * name, struct group *grp, char *buffer, size_t bufsize, struct group **result);
The getgrnam() function shall search the group database for an entry with a matching name.
The getgrnam() function need not be thread-safe.
The getgrnam_r() function shall update the group structure pointed to by grp and store a pointer to that structure at the location pointed to by result. The structure shall contain an entry from the group database with a matching name. Storage referenced by the group structure is allocated from the memory provided with the buffer parameter, which is bufsize bytes in size. A call to sysconf(_SC_GETGR_R_SIZE_MAX) returns either −1 without changing errno or an initial value suggested for the size of this buffer. A null pointer is returned at the location pointed to by result on error or if the requested entry is not found.
The getgrnam() function shall return a pointer to a struct group with the structure defined in <grp.h> with a matching entry if one is found. The getgrnam() function shall return a null pointer if either the requested entry was not found, or an error occurred. On error, errno shall be set to indicate the error.
The application shall not modify the structure to which the return value points, nor any storage areas pointed to by pointers within the structure. The returned pointer, and pointers within the structure, might be invalidated or the structure or the storage areas might be overwritten by a subsequent call to getgrent(), getgrgid(), or getgrnam().
The getgrnam_r() function shall return zero on success or if the requested entry was not found and no error has occurred. If any error has occurred, an error number shall be returned to indicate the error.
The getgrnam() and getgrnam_r() functions may fail if:
- An I/O error has occurred.
- A signal was caught during getgrnam().
- All file descriptors available to the process are currently open.
The getgrnam_r() function may fail if:
- The maximum allowable number of files is currently open in the system.
The following sections are informative.
Note that sysconf(_SC_GETGR_R_SIZE_MAX) may return −1 if there is no hard limit on the size of the buffer needed to store all the groups returned. This example shows how an application can allocate a buffer of sufficient size to work with getgrnam_r().
- Insufficient storage was supplied via buffer and bufsize to contain the data to be referenced by the resulting group structure.
Applications wishing to check for error situations should set errno to 0 before calling getgrnam(). If errno is set on return, an error occurred.
The getgrnam_r() function is thread-safe and shall return values in a user-supplied buffer instead of possibly using a static data area that may be overwritten by each call.
Portable applications should take into account that it is usual for an implementation to return −1 from sysconf() indicating that there is no maximum for _SC_GETGR_R_SIZE_MAX.
endgrent(), getgrgid(), sysconf()
The Base Definitions volume of POSIX.1‐2008, <grp.h>, <sys_types.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
long int initlen = sysconf(_SC_GETGR_R_SIZE_MAX);
if (initlen == −1)
/* Default initial length. */
len = 1024;
len = (size_t) initlen;
struct group result;
struct group *resultp;
char *buffer = malloc(len);
if (buffer == NULL)
while ((e = getgrnam_r("somegroup", &result, buffer, len, &resultp))
size_t newlen = 2 * len;
if (newlen < len)
len = newlen;
char *newbuffer = realloc(buffer, len);
if (newbuffer == NULL)
buffer = newbuffer;
if (e != 0)
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