A.10 smbd

Synopsis

 smbd [-D] [-F] [-S] [-i] [-h] [-V] [-b] [-d <debug level>] [-l <log directory>] [-p <port number>] [-O <socket option>] [-s <configuration file>]

Description

This program is part of the Samba(7) suite.

smbd is the server daemon that provides filesharing and printing services to Windows clients. The server provides filespace and printer services to clients using the SMB (or CIFS) protocol. This is compatible with the LanManager protocol, and can service LanManager clients . These include MSCLIENT 3.0 for DOS, Windows for Workgroups, Windows 95/98/ME, Windows NT, Windows 2000, OS/2, DAVE for Macintosh, and smbfs for Linux.

An extensive description of the services that the server can provide is given in the man page for the configuration file controlling the attributes of those services (see smb.conf(5). This man page will not describe the services, but will concentrate on the administrative aspects of running the server.

Please note that there are significant security implications to running this server, and the smb.conf(5) manual page should be regarded as mandatory reading before proceeding with installation.

A session is created whenever a client requests one. Each client gets a copy of the server for each session. This copy then services all connections made by the client during that session. When all connections from its client are closed, the copy of the server for that client terminates.

The configuration file, and any files that it includes, are automatically reloaded every minute, if they change. You can force a reload by sending a SIGHUP to the server. Reloading the configuration file will not affect connections to any service that is already established. Either the user will have to disconnect from the service, or smbd killed and restarted.

Options

-D ” If specified, this parameter causes the server to operate as a daemon. That is, it detaches itself and runs in the background, fielding requests on the appropriate port. Operating the server as a daemon is the recommended way of running smbd for servers that provide more than casual use file and print services. This switch is assumed if smbd is executed on the command line of a shell.

-F ” If specified, this parameter causes the main smbd process to not daemonize, i.e. double-fork and disassociate with the terminal. Child processes are still created as normal to service each connection request, but the main process does not exit. This operation mode is suitable for running smbd under process supervisors such as supervise and svscan from Daniel J. Bernstein's daemontools package, or the AIX process monitor.

-S ” If specified, this parameter causes smbd to log to standard output rather than a file.

-i ” If this parameter is specified it causes the server to run "interactively", not as a daemon, even if the server is executed on the command line of a shell. Setting this parameter negates the implicit deamon mode when run from the command line. smbd also logs to standard output, as if the -S parameter had been given.

-V ” Prints the program version number.

-s <configuration file> ” The file specified contains the configuration details required by the server. The information in this file includes server-specific information such as what printcap file to use, as well as descriptions of all the services that the server is to provide. See smb.conf for more information. The default configuration file name is determined at compile time.

-d “debug=debuglevel ” debuglevel is an integer from 0 to 10. The default value if this parameter is not specified is zero.

The higher this value, the more detail will be logged to the log files about the activities of the server. At level 0, only critical errors and serious warnings will be logged. Level 1 is a reasonable level for day-to-day running - it generates a small amount of information about operations carried out.

Levels above 1 will generate considerable amounts of log data, and should only be used when investigating a problem. Levels above 3 are designed for use only by developers and generate HUGE amounts of log data, most of which is extremely cryptic.

Note that specifying this parameter here will override the log level parameter in the smb.conf file.

-l “logfile=logbasename ” File name for log/debug files. The extension ".client" will be appended. The log file is never removed by the client.

-h “help ” Print a summary of command line options.

-b ” Prints information about how Samba was built.

-l <log directory> ” If specified, log directory specifies a log directory into which the "log.smbd" log file will be created for informational and debug messages from the running server. The log file generated is never removed by the server although its size may be controlled by the max log size option in the smb.conf(5) file. Beware: If the directory specified does not exist, smbd will log to the default debug log location defined at compile time.

The default log directory is specified at compile time.

-p <port number> ” port number is a positive integer value. The default value if this parameter is not specified is 139.

This number is the port number that will be used when making connections to the server from client software. The standard (well-known) port number for the SMB over TCP is 139, hence the default. If you wish to run the server as an ordinary user rather than as root, most systems will require you to use a port number greater than 1024 - ask your system administrator for help if you are in this situation.

In order for the server to be useful by most clients, should you configure it on a port other than 139, you will require port redirection services on port 139, details of which are outlined in rfc1002.txt section 4.3.5.

This parameter is not normally specified except in the above situation.

Files

/etc/inetd.conf ” If the server is to be run by the inetd meta-daemon, this file must contain suitable startup information for the meta-daemon.

/etc/rc ” or whatever initialization script your system uses).

If running the server as a daemon at startup, this file will need to contain an appropriate startup sequence for the server.

/etc/services ” If running the server via the meta-daemon inetd , this file must contain a mapping of service name (e.g., netbios-ssn) to service port (e.g., 139) and protocol type (e.g., tcp).

/usr/local/samba/lib/smb.conf ” This is the default location of the smb.conf(5) server configuration file. Other common places that systems install this file are /usr/samba/lib/smb.conf and /etc/samba/smb.conf .

This file describes all the services the server is to make available to clients. See smb.conf(5) for more information.

Limitations

On some systems smbd cannot change uid back to root after a setuid() call. Such systems are called trapdoor uid systems. If you have such a system, you will be unable to connect from a client (such as a PC) as two different users at once. Attempts to connect the second user will result in access denied or similar.

Environment Variables

PRINTER ” If no printer name is specified to printable services, most systems will use the value of this variable (or lp if this variable is not defined) as the name of the printer to use. This is not specific to the server, however.

PAM Interaction

Samba uses PAM for authentication (when presented with a plaintext password), for account checking (is this account disabled?) and for session management. The degree too which samba supports PAM is restricted by the limitations of the SMB protocol and the obey pam restrictions smb.conf(5) paramater. When this is set, the following restrictions apply:

Account Validation : All accesses to a samba server are checked against PAM to see if the account is vaild, not disabled and is permitted to login at this time. This also applies to encrypted logins.
Session Management : When not using share level secuirty, users must pass PAM's session checks before access is granted. Note however, that this is bypassed in share level secuirty. Note also that some older pam configuration files may need a line added for session support.

Diagnostics

Most diagnostics issued by the server are logged in a specified log file. The log file name is specified at compile time, but may be overridden on the command line.

The number and nature of diagnostics available depends on the debug level used by the server. If you have problems, set the debug level to 3 and peruse the log files.

Most messages are reasonably self-explanatory. Unfortunately, at the time this man page was created, there are too many diagnostics available in the source code to warrant describing each and every diagnostic. At this stage your best bet is still to grep the source code and inspect the conditions that gave rise to the diagnostics you are seeing.

Signals

Sending the smbd a SIGHUP will cause it to reload its smb.conf configuration file within a short period of time.

To shut down a user's smbd process it is recommended that SIGKILL (-9) NOT be used, except as a last resort, as this may leave the shared memory area in an inconsistent state. The safe way to terminate an smbd is to send it a SIGTERM (-15) signal and wait for it to die on its own.

The debug log level of smbd may be raised or lowered using smbcontrol (1) program (SIGUSR[12] signals are no longer used since Samba 2.2). This is to allow transient problems to be diagnosed, whilst still running at a normally low log level.

Note that as the signal handlers send a debug write, they are not re-entrant in smbd . This you should wait until smbd is in a state of waiting for an incoming SMB before issuing them. It is possible to make the signal handlers safe by un-blocking the signals before the select call and re-blocking them after, however this would affect performance.