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getnetent(3) Library Functions Manual getnetent(3)


getnetent, getnetbyname, getnetbyaddr, setnetent, endnetent - get network entry


Standard C library (libc, -lc)


#include <netdb.h>
struct netent *getnetent(void);
struct netent *getnetbyname(const char *name);
struct netent *getnetbyaddr(uint32_t net, int type);
void setnetent(int stayopen);
void endnetent(void);


The getnetent() function reads the next entry from the networks database and returns a netent structure containing the broken-out fields from the entry. A connection is opened to the database if necessary.

The getnetbyname() function returns a netent structure for the entry from the database that matches the network name.

The getnetbyaddr() function returns a netent structure for the entry from the database that matches the network number net of type type. The net argument must be in host byte order.

The setnetent() function opens a connection to the database, and sets the next entry to the first entry. If stayopen is nonzero, then the connection to the database will not be closed between calls to one of the getnet*() functions.

The endnetent() function closes the connection to the database.

The netent structure is defined in <netdb.h> as follows:

struct netent {

char *n_name; /* official network name */
char **n_aliases; /* alias list */
int n_addrtype; /* net address type */
uint32_t n_net; /* network number */ }

The members of the netent structure are:

The official name of the network.
A NULL-terminated list of alternative names for the network.
The type of the network number; always AF_INET.
The network number in host byte order.


The getnetent(), getnetbyname(), and getnetbyaddr() functions return a pointer to a statically allocated netent structure, or a null pointer if an error occurs or the end of the file is reached.


networks database file


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

Interface Attribute Value
getnetent () Thread safety MT-Unsafe race:netent race:netentbuf env locale
getnetbyname () Thread safety MT-Unsafe race:netbyname env locale
getnetbyaddr () Thread safety MT-Unsafe race:netbyaddr locale
setnetent (), endnetent () Thread safety MT-Unsafe race:netent env locale

In the above table, netent in race:netent signifies that if any of the functions setnetent(), getnetent(), or endnetent() are used in parallel in different threads of a program, then data races could occur.




POSIX.1-2001, 4.3BSD.

Before glibc 2.2, the net argument of getnetbyaddr() was of type long.


getnetent_r(3), getprotoent(3), getservent(3)
RFC 1101

2023-07-20 Linux man-pages 6.05.01