GETGRNAM(3POSIX)

💖 GETGRNAM — search group database for a name 💖

okay bestie, gather round, because we're looking up groups today and it's giving database detective energy 🔍✨

this page lives in the POSIX Programmer's Manual, bestie. noted. 💅

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🌸 PROLOG 🌸

okay so first things first, a lil heads up: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, consult the corresponding Linux manual page for details of Linux behavior), or the interface may not even be implemented on Linux. not me warning you before you even start 😭 read the right page for your platform, fr fr.

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✨ NAME ✨

getgrnam, getgrnam_r — search group database for a name 🫶

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🎀 SYNOPSIS 🎀

#include <grp.h>

struct group *getgrnam(const char *name);
int getgrnam_r(const char *name, struct group *grp, char *buffer,
    size_t bufsize, struct group **result);

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🦋 DESCRIPTION 🦋

so the getgrnam() function shall search the group database for an entry with a matching name. that's the whole vibe. 💫

lowkey important: the getgrnam() function need not be thread-safe. 🚨 like, it's not obligated to be safe across threads, so don't come for it.

if you're an application and you wanna check for error situations, you should set errno to 0 before calling getgrnam(). then: if getgrnam() returns a null pointer and errno is set to non-zero, an error occurred. simple as. ⭐

now the _r version, which is the main character honestly 👑 — 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. That 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. and here's a lil gem: 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. so like, always check your result, bestie 💀

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💜 RETURN VALUE 💜

getgrnam() shall return a pointer to a struct group with the structure defined in <grp.h> with a matching entry if one is found. and if nothing's found or something went wrong? null pointer. periodt. specifically: the getgrnam() function shall return a null pointer if either the requested entry was not found, or an error occurred. If the requested entry was not found, errno shall not be changed. On error, errno shall be set to indicate the error. 📝

⚠️ okay this part is SO important, do not skip it bestie: 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 returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated. 😭 so like, copy what you need while you can, bestie, because this data is fleeting.

and for getgrnam_r(): it 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. 🌈

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🔥 ERRORS 🔥

the getgrnam() and getgrnam_r() functions may fail if:

• EIO — An I/O error has occurred. 💀
• EINTR — A signal was caught during getgrnam().
• EMFILE — All file descriptors available to the process are currently open.
• ENFILE — The maximum allowable number of files is currently open in the system.

and the getgrnam_r() function may fail if:

• ERANGE — Insufficient storage was supplied via buffer and bufsize to contain the data to be referenced by the resulting group structure. (translation: your buffer was too smol 😭 grow it)

The following sections are informative.

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🍓 EXAMPLES 🍓

okay so note this: 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(). iconic behaviour honestly 👑

    long int initlen = sysconf(_SC_GETGR_R_SIZE_MAX);
    size_t len;
    if (initlen == -1)
        /* Default initial length. */
        len = 1024;
    else
        len = (size_t) initlen;
    struct group result;
    struct group *resultp;
    char *buffer = malloc(len);
    if (buffer == NULL)
        ...handle error...
    int e;
    while ((e = getgrnam_r("somegroup", &result, buffer, len, &resultp))
            == ERANGE)
        {
        size_t newlen = 2 * len;
        if (newlen < len)
            ...handle error...
        len = newlen;
        char *newbuffer = realloc(buffer, len);
        if (newbuffer == NULL)
            ...handle error...
        buffer = newbuffer;
        }
    if (e != 0)
        ...handle error...
    free (buffer);

see how it just keeps doubling until ERANGE stops happening? that's the loop, bestie. the way that it reallocs and retries… we love a resilient queen 💅

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🌈 APPLICATION USAGE 🌈

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. so if you're multithreaded, _r is your girl 🫶

also, 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. so like, don't panic when you see that -1, it's normal 🧚✨

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⭐ RATIONALE ⭐

None. (nothing here bestie, it's a vibe-free zone 🙈)

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🌸 FUTURE DIRECTIONS 🌸

None. (also empty, we're just chillin 🎀)

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💫 SEE ALSO 💫

• endgrent()
• getgrgid()
• sysconf()

The Base Definitions volume of POSIX.1‐2017, <grp.h>, <sys_types.h> 📚

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👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page bestie!! 💖✨ this one came from IEEE/The Open Group, 2017 — mwah, ty for the lore, go look up your groups responsibly 🎀🦋💅