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GETSERVENT(3) Library Functions Manual GETSERVENT(3)

getservent, getservent_r, getservbyport, getservbyport_r, getservbyname, getservbyname_r, setservent, endservent — get service entry

library “libc”

#include <netdb.h>

struct servent *
getservent(void);

int
getservent_r(struct servent *, char *, size_t, struct servent **);

struct servent *
getservbyname(const char *name, const char *proto);

int
getservbyname_r(const char *, const char *, struct servent *, char *, size_t, struct servent **);

struct servent *
getservbyport(int port, const char *proto);

int
getservbyport_r(int, const char *, struct servent *, char *, size_t, struct servent **);

void
setservent(int stayopen);

void
endservent(void);

The (), getservbyname(), and getservbyport() functions each return a pointer to an object with the following structure containing the broken-out fields of a line in the network services data base, /etc/services. 
struct	servent {
	char	*s_name;	/* official name of service */
	char	**s_aliases;	/* alias list */
	int	s_port;		/* port service resides at */
	char	*s_proto;	/* protocol to use */
};

The members of this structure are:

s_name
The official name of the service.
s_aliases
A zero terminated list of alternate names for the service.
s_port
The port number at which the service resides. Port numbers are returned in network byte order.
s_proto
The name of the protocol to use when contacting the service.

The () function reads the next line of the file, opening the file if necessary.

The () function opens and rewinds the file. If the stayopen flag is non-zero, the net data base will not be closed after each call to getservbyname() or getservbyport().

The () function closes the file.

The () and () functions sequentially search from the beginning of the file until a matching protocol name or port number (which must be specified in network byte order) is found, or until EOF is encountered. If a protocol name is also supplied (non- NULL), searches must also match the protocol.

The (), (), and () functions are reentrant versions of the above functions that take a pointer to a servent structure which is used to store state information. The structure must be zero-filled before it is used and should be considered opaque for the sake of portability. These functions also take a pointer to another servent structure which is used to store the results of the database lookup.

The getservent(), getservbyport(), and getservbyname() functions return a pointer to a servent structure on success or a null pointer if end-of-file is reached or an error occurs.

The getservent_r(), getservbyport_r(), and getservbyname_r() functions return 0 on success or -1 if end-of-file is reached or an error occurs.

/etc/services
 

getprotoent(3), services(5)

The getservent(), getservbyport(), getservbyname(), setservent(), and endservent() functions conform to IEEE Std 1003.1-2004 (“POSIX.1”).

The getservent_r(), getservbyport_r(), and getservbyname_r() functions are not currently standardized.

The getservent(), getservbyport(), getservbyname(), setservent(), and endservent() functions appeared in 4.2BSD.

The getservent_r(), getservbyport_r(), and getservbyname_r() functions appeared in DragonFly 2.1.

These functions use a thread-specific data storage; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Expecting port numbers to fit in a 32 bit quantity is probably naive.

May 4, 2019 DragonFly-5.6.1