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Manual Reference Pages  -  LIBSERVER (8)


libserver - Generic Server Library


     Access To Configuration Variables
     Threaded Servers
     Command-line Options


#include <libserver.h> (-pthread) -I/usr/local/include -L/usr/local/lib -lserver(threads)


The Libserver package supplies 3 libraries that implement generic servers. The libraries perform network and concurrency tasks. You supply code to service connections. All 3 libraries service TCP or UNIX-domain connections. Separate libraries implement multi-process, multi-threaded, and event-driven servers. This manual documents the multi-process and multi-threaded libraries. The event-driven library is described in the "libserverevents" manual.

To create a multi-process server, link with -lserver. To create a multi-threaded server, link with -lserverthreads.

Example echo servers are included in the libserver source distribution.


The libraries provide your server’s "main" function. You define 3 functions to match the following prototypes.
void serv_init_func();
void serv_worker_init_func();
void serv_service_connection( FILE * );

Do not define any other global symbol beginning with the five characters 'serv_’ because the library reserves that namespace.


One master process/thread grows and shrinks a pool of workers to service connections. Workers call serv_service_connection() once to service each connection that they accept. Workers close connections when serv_service_connection() returns.

serv_service_connection() is invoked with the FILE pointer of a buffered stream that is connected to the client. You use the standard buffered IO functions to communicate with the client. If you want to use non-buffered IO, use the fileno() function to determine the descriptor that is associated with the FILE pointer. Do not close the FILE pointer or its underlying descriptor, or you will crash your server.


In serv_init_func() perform the initialization tasks your server needs to do once at server start-up before any workers are created.

The library calls serv_init_func():

  • after changing to the directory specified by the -r command line option.
  • before attempting to change the server’s user and group to the values specified by the command line options. If the server starts as root serv_init_func(), executes as root.
  • before the server becomes a daemon and starts listening for connections. The standard streams are connected to the terminal from which the server was started. Error and informative messages should be sent to the terminal.


Call serv_set_name() inside serv_init_func() to set the server’s name.
void serv_set_name( char * );

If not set the server’s name defaults to "server". The server’s name is used in two ways:

  • When the server is running, stderr is connected to /dev/null. Errors must are reported with syslog(3). The library calls openlog() with the server’s name as argument to ensure that log entries are identified by the server’s name.
  • The server’s pidfile is written to /var/run/ if the server is started as root. The filename is the server’s name with ".pid" appended to it. This file is used by rc.d scripts to stop the server. A sample script is included in the libserver distribution.


In serv_init_func(), you can install a function for the master to invoke periodically with:
void serv_set_periodic( void (*)(), int );

The function pointed to by first argument is called when the number of seconds specified by the second argument have elapsed and then again repeatedly when that number of seconds has elapsed since the last call.


In serv_worker_init_func() perform the initialization tasks each worker needs to perform independently of the master. For example, open unique database connections for each worker in serv_worker_init_func().

serv_worker_init_func() is called after:

  • the user and group of the process have been changed to the values specified by the -u and -g command line options.
  • the standard streams are connected to /dev/null. Errors must be reported with syslog(3).


Both libraries need to catch SIGTERM, so do not change the disposition of that signal.

The multi-threaded library additionally needs to catch SIGUSR1, so do not change the disposition of that signal in multi-threaded servers.

Upon receipt of SIGBUS or SIGSEGV, libserver restarts servers with a call to execv(3). If you want to do something else, install your own handler.

If your server starts as root and changes user and group, the library will be unable to restart if your server is not executable by the user or group.

The library will be unable to perform the operations that require root privileges after restart unless you turn on the setuid bit of the server (chmod u=+s).


You can examine the following configuration variables from your code, but you must not modify them. See the CONFIGURATION section for more information.
char *serv_config_file;
char *serv_root_dir;
char *serv_interface;
char *serv_port;
char *serv_user;
char *serv_group;

  points to the value passed to the -f option. Defaults to NULL.
serv_root_dir points to the value passed to the -r option. Defaults to NULL.
serv_interface points to the value passed to the -i option. Defaults to "".
serv_port points to the value passed as argument to the -p option. Defaults to "1966".
serv_user points to the value passed as argument to the -u option. Defaults to "nobody".
serv_group points to the value passed as argument to the -g option. Defaults to "nobody".


If your threaded server encounters an unrecoverable error call serv_thread_exit() in the thread with the error. DO NOT call pthread_exit() directly.
void serv_thread_exit();

To create and manage globally-visible data that is unique for each connection use the pthread thread-specific data functions. The following are the minimal set of functions that you need to understand. All are documented in manual pages.


Each thread maps keys to its thread-specific storage space.

  • In scgi_init_func(), create your keys with pthread_key_create(). Pass a destructor function to pthread_key_create() to free the space workers associate with keys, or your server will leak memory on thread termination.
  • In scgi_worker_init_func(), malloc(3) the current thread’s thread-specific storage and install it with pthread_setspecific().
  • In scgi_request_handler(), retrieve your thread-specific storage with pthread_getspecific(). Put fresh data in your storage as you like in each invocation of scgi_request_handler().
  • Release any dynamically allocated storage that are not freed by your keys’ destructors before returning from scgi_request_handler().


Libserver writes its pidfile into /var/run/ if is started as root. The library is stopped with SIGTERM. Libserver does graceful stops. Idle workers exit immediately. Workers with established connections continue to service those connections until they close. If you want to kill a server outright, send it a SIGKILL. A sample control script is provided in the server distribution. To use the script, you must replace all occurrences of "server" with the value you pass to serv_set_name(). The script must be renamed as the value you passed to serv_set_name() and installed in /usr/local/etc/rc.d.

Two variables must be added to /etc/rc.conf to use the script. Substitute your server’s name for "server":

server_flags="-u www -g www -r /usr/local/server"

If the "enable" variable is set to "YES", the server is started at system start. Use the following rc commands:

/usr/local/etc/rc.d/server start
/usr/local/etc/rc.d/server stop
/usr/local/etc/rc.d/server restart
/usr/local/etc/rc.d/server status

If you do not want the server started on system start, then set


and use the following commands:

/usr/local/etc/rc.d/server forcestart
/usr/local/etc/rc.d/server forcestop
/usr/local/etc/rc.d/server forcerestart
/usr/local/etc/rc.d/server forcestatus

Servers do not exit until all threads with active connections have closed those connections. To prevent idle connections from delaying exit indefinitely, place a timeout on socket reads or writes with setsockopt(). Placing a read timeout on a socket is demonstrated in the echo_tls.c example program included in the libserver source distribution.


The following command line options are recognized by libserver servers. All of these are optional.
-r User the -r option to specify the server root directory. Libserver chdir(2)s there.
-l By default, the library listens on all TCP interfaces it can find capable of IPv4 or IPv6. The -l option instructs the library to listen on a UNIX-domain socket instead. Specify the path to the socket as argument. The server creates the socket when it starts, unlinking it first if it already exists in the filesystem. The owner and group of the socket are changed to the values of the -u and -g options. The permisssions of the socket are set to srwxrwx---. You cannot specify the -l option together with the -p or -i options.
-p The -p option specifies the port to listen on. This defaults to 1966. To bind to a port lower than 1024, the server must be started as root.
-i By default, libserver accepts connections on all interfaces it can find capable of IPv4 or IPv6. The -i option limits libserver to accepting connections from a specified interface. Pass the IP address of the desired interface as argument.
-n The -n options specifies the number of idle workers the master keeps ready. the value defaults to 5. The library actually allows the number of idle workers to reach half this value before it creates more.
-m The -m option specifies the maximum number of workers which may be running at any time. The value defaults to 25. This value is the maximum number of simultaneous connections a server can accept. The value specified must be equal to or greater than the value specified for -n.
-q The -q option specifies the backlog of client connections queued by the OS kernel for the server to subsequently service. This value defaults to 1024. Note that the kernel actually uses a queue of 1.5 times the size of the specified value. Connections arriving when the queue is full are dropped by the kernel. Libserver does not let you set this value to less than 1024.
  The -u and the -g options are used to specify the user and group for the server. Both values default to "nobody". For libserver to change user, it must be started as root.

Libserver restarts servers on receipt of SIGSEGV or SIGBUS.

If your server starts as root and changes user and group, the library will be unable to restart if your server is not executable by the user or group.

The library will be unable to perform the operations that require root privileges after restart unless you turn on the setuid bit of the server (chmod +s).

-x The -x option prevents libserver from becoming a daemon and writing its pidfile to /var/run/. Libserver runs in the foreground. Stderr is connected to the terminal so that diagnostic output can be sent there.
-t The -t option is only available to threaded servers and causes those servers to exit immediately when they receive SIGTERM. Normally, threaded servers postpone exiting until all established connections have closed naturally.
-f The -f option takes a filename as argument. Libserver assigns the filename to the global character pointer serv_config_file. This enables code in serv_init_func() and serv_worker_init_func() to access a configuration file.


.An James Bailie Aq
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