---
name: "getgrent_r"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/getgrent_r"
---

# getgrent\_r(3)

get group file entry reentrantly

## NAME

getgrent\_r, fgetgrent\_r - get group file entry reentrantly

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <grp.h>
```

**int getgrent\_r(**size\_t size;                **struct group \*restrict** *gbuf***,**                **char** *buf***\[restrict** *size***\], size\_t** *size***,**                **struct group \*\*restrict** *gbufp***);** **int fgetgrent\_r(**size\_t size;                **FILE \*restrict** *stream***, struct group \*restrict** *gbuf***,**                **char** *buf***\[restrict** *size***\], size\_t** *size***,**                **struct group \*\*restrict** *gbufp***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**getgrent\_r**():

```
    _GNU_SOURCE
```

**fgetgrent\_r**():

```
    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _SVID_SOURCE
```

## DESCRIPTION

The functions **getgrent\_r**() and **fgetgrent\_r**() are the reentrant versions of [**getgrent**(3)](/getgrent/3.md) and [**fgetgrent**(3)](/fgetgrent/3.md). The former reads the next group entry from the stream initialized by [**setgrent**(3)](/setgrent/3.md). The latter reads the next group entry from *stream*.

The *group* structure is defined in *\<grp.h\>* as follows:

```
struct group {
    char   *gr_name;        /* group name */
    char   *gr_passwd;      /* group password */
    gid_t   gr_gid;         /* group ID */
    char  **gr_mem;         /* NULL-terminated array of pointers
                               to names of group members */
};
```

For more information about the fields of this structure, see [**group**(5)](/group/5.md).

The nonreentrant functions return a pointer to static storage, where this static storage contains further pointers to group name, password, and members. The reentrant functions described here return all of that in caller-provided buffers. First of all there is the buffer *gbuf* that can hold a *struct group*. And next the buffer *buf* of size *size* that can hold additional strings. The result of these functions, the *struct group* read from the stream, is stored in the provided buffer *\*gbuf*, and a pointer to this *struct group* is returned in *\*gbufp*.

## RETURN VALUE

On success, these functions return 0 and *\*gbufp* is a pointer to the *struct group*. On error, these functions return an error value and *\*gbufp* is NULL.

## ERRORS

- **ENOENT**

  No more entries.

- **ERANGE**

  Insufficient buffer space supplied. Try again with larger buffer.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **getgrent\_r**() | Thread safety | MT-Unsafe race:grent locale |
| **fgetgrent\_r**() | Thread safety | MT-Safe |

In the above table, *grent* in *race:grent* signifies that if any of the functions [**setgrent**(3)](/setgrent/3.md), [**getgrent**(3)](/getgrent/3.md), [**endgrent**(3)](/endgrent/3.md), or **getgrent\_r**() are used in parallel in different threads of a program, then data races could occur.

## VERSIONS

Other systems use the prototype

```
struct group *getgrent_r(struct group *grp, char buf[.size],
                         int size);
```

or, better,

```
int getgrent_r(struct group *grp, char buf[.size], int size,
               FILE **gr_fp);
```

## STANDARDS

GNU.

## HISTORY

These functions are done in a style resembling the POSIX version of functions like [**getpwnam\_r**(3)](/getpwnam_r/3.md).

## NOTES

The function **getgrent\_r**() is not really reentrant since it shares the reading position in the stream with all other threads.

## EXAMPLES

```
#define _GNU_SOURCE
#include <grp.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFLEN 4096
int
main(void)
{
    struct group grp;
    struct group *grpp;
    char buf[BUFLEN];
    int i;
    setgrent();
    for (;;) {
        i = getgrent_r(&grp, buf, sizeof(buf), &grpp);
        if (i)
            break;
        printf("%s (%jd):", grpp->gr_name, (intmax_t) grpp->gr_gid);
        for (size_t j = 0; ; j++) {
            if (grpp->gr_mem[j] == NULL)
                break;
            printf(" %s", grpp->gr_mem[j]);
        }
        printf("\n");
    }
    endgrent();
    exit(EXIT_SUCCESS);
}
```

## SEE ALSO

[**fgetgrent**(3)](/fgetgrent/3.md), [**getgrent**(3)](/getgrent/3.md), [**getgrgid**(3)](/getgrgid/3.md), [**getgrnam**(3)](/getgrnam/3.md), [**putgrent**(3)](/putgrent/3.md), [**group**(5)](/group/5.md)