setnetgrent, endnetgrent, getnetgrent, getnetgrent_r, innetgr - handle network group entries


Standard C library (libc, -lc)


#include <netdb.h>
int setnetgrent(const char *netgroup);
void endnetgrent(void);
int getnetgrent(char **restrict host,
 char **restrict user, char **restrict domain);
int getnetgrent_r(char **restrict host,
 char **restrict user, char **restrict domain,
 char buf[restrict .buflen], size_t buflen);
int innetgr(const char *netgroup, const char *host,
 const char *user, const char *domain);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

setnetgrent(), endnetgrent(), getnetgrent(), getnetgrent_r(), innetgr():

    Since glibc 2.19:
    glibc 2.19 and earlier:


The netgroup is a SunOS invention. A netgroup database is a list of string triples (hostname, username, domainname) or other netgroup names. Any of the elements in a triple can be empty, which means that anything matches. The functions described here allow access to the netgroup databases. The file /etc/nsswitch.conf defines what database is searched.

The setnetgrent() call defines the netgroup that will be searched by subsequent getnetgrent() calls. The getnetgrent() function retrieves the next netgroup entry, and returns pointers in host, user, domain. A null pointer means that the corresponding entry matches any string. The pointers are valid only as long as there is no call to other netgroup-related functions. To avoid this problem you can use the GNU function getnetgrent_r() that stores the strings in the supplied buffer. To free all allocated buffers use endnetgrent().

In most cases you want to check only if the triplet (hostname, username, domainname) is a member of a netgroup. The function innetgr() can be used for this without calling the above three functions. Again, a null pointer is a wildcard and matches any string. The function is thread-safe.


These functions return 1 on success and 0 for failure.




For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value

setnetgrent(), getnetgrent_r(), innetgr()

Thread safety

MT-Unsafe race:netgrent locale


Thread safety

MT-Unsafe race:netgrent


Thread safety

MT-Unsafe race:netgrent race:netgrentbuf locale

In the above table, netgrent in race:netgrent signifies that if any of the functions setnetgrent(), getnetgrent_r(), innetgr(), getnetgrent(), or endnetgrent() are used in parallel in different threads of a program, then data races could occur.


In the BSD implementation, setnetgrent() returns void.




setnetgrent(), endnetgrent(), getnetgrent(), and innetgr() are available on most UNIX systems. getnetgrent_r() is not widely available on other systems.


sethostent(3), setprotoent(3), setservent(3)