smbd (8)

NAME
smbd - server to provide SMB/CIFS services to clients

SYNOPSIS

smbd [-D] [-a] [-o] [-d debuglevel] [-l log file] [-p port number] [-O socket options] [-s configuration file] [-i scope] [-P] [-h]

DESCRIPTION

This program is part of the Samba 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, Windows NT, 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) manpage 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.

    By default, the server will NOT operate as a daemon.

-a  If this parameter is specified, each new connection will append log messages to the log file. This is the default.

-o  If this parameter is specified, the log files will be overwritten when opened. By default, the log files will be appended to.

-d 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 (5) file.

-l log file
    If specified, log file specifies a log filename into which informational and debug messages from the running server will be logged. 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. The default log file name is specified at compile time.

-O socket options
    See the socket options parameter in the smb.conf (5) file for details.

-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.

-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 (5) for more information. The default configuration file name is determined at compile time.

-i scope
    This specifies a NetBIOS scope that the server will use to communicate with when generating NetBIOS names. For details on the use of NetBIOS scopes, see rfc1001.txt and rfc1002.txt. NetBIOS scopes are very rarely used, only set this parameter if you are the system administrator in charge of all the NetBIOS systems you communicate with.

-h  Prints the help information (usage) for smbd.

-P  Passive option. Causes smbd not to send any network traffic out. Used for debugging by the developers only.

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. See the section INSTALLATION below.

/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. See the section INSTALLATION below.

/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). See the section INSTALLATION below.

/usr/local/samba/lib/smb.conf

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

INSTALLATION

The location of the server and its support files is a matter for individual system administrators. The following are thus suggestions only.

It is recommended that the server software be installed under the /usr/local/samba hierarchy, in a directory readable by all, writeable only by root. The server program itself should be executable by all, as users may wish to run the server themselves (in which case it will of course run with their privileges). The server should NOT be setuid. On some systems it may be worthwhile to make smbd setgid to an empty group. This is because some systems may have a security hole where daemon processes that become a user can be attached to with a debugger. Making the smbd file setgid to an empty group may prevent this hole from being exploited. This security hole and the suggested fix has only been confirmed on old versions (pre-kernel 2.0) of Linux at the time this was written. It is possible that this hole only exists in Linux, as testing on other systems has thus far shown them to be immune.

The server log files should be put in a directory readable and writeable only by root, as the log files may contain sensitive information.

The configuration file should be placed in a directory readable and writeable only by root, as the configuration file controls security for the services offered by the server. The configuration file can be made readable by all if desired, but this is not necessary for correct operation of the server and is not recommended. A sample configuration file "smb.conf.sample" is supplied with the source to the server - this may be renamed to "smb.conf" and modified to suit your needs.

The remaining notes will assume the following:

o   smbd (the server program) installed in /usr/local/samba/bin

o   smb.conf (the configuration file) installed in /usr/local/samba/lib

o   log files stored in /var/adm/smblogs

The server may be run either as a daemon by users or at startup, or it may be run from a meta-daemon such as inetd upon request. If run as a daemon, the server will always be ready, so starting sessions will be faster. If run from a meta-daemon some memory will be saved and utilities such as the tcpd TCP-wrapper may be used for extra security. For serious use as file server it is recommended that smbd be run as a daemon.

When you've decided, continue with either RUNNING THE SERVER AS A DAEMON or RUNNING THE SERVER ON REQUEST.

RUNNING THE SERVER AS A DAEMON

To run the server as a daemon from the command line, simply put the -D option on the command line. There is no need to place an ampersand at the end of the command line - the -D option causes the server to detach itself from the tty anyway.

Any user can run the server as a daemon (execute permissions permitting, of course). This is useful for testing purposes, and may even be useful as a temporary substitute for something like ftp. When run this way, however, the server will only have the privileges of the user who ran it.

To ensure that the server is run as a daemon whenever the machine is started, and to ensure that it runs as root so that it can serve multiple clients, you will need to modify the system startup files. Wherever appropriate (for example, in /etc/rc), insert the following line, substituting port number, log file location, configuration file location and debug level as desired:

/usr/local/samba/bin/smbd -D -l /var/adm/smblogs/log -s /usr/local/samba/lib/smb.conf

(The above should appear in your initialization script as a single line. Depending on your terminal characteristics, it may not appear that way in this man page. If the above appears as more than one line, please treat any newlines or indentation as a single space or TAB character.)

If the options used at compile time are appropriate for your system, all parameters except -D may be omitted. See the section OPTIONS above.

RUNNING THE SERVER ON REQUEST

If your system uses a meta-daemon such as inetd, you can arrange to have the smbd server started whenever a process attempts to connect to it. This requires several changes to the startup files on the host machine. If you are experimenting as an ordinary user rather than as root, you will need the assistance of your system administrator to modify the system files.

You will probably want to set up the NetBIOS name server nmbd at the same time as smbd. To do this refer to the man page for nmbd (8).

First, ensure that a port is configured in the file /etc/services. The well-known port 139 should be used if possible, though any port may be used.

Ensure that a line similar to the following is in /etc/services:

netbios-ssn    139/tcp

Note for NIS/YP users - you may need to rebuild the NIS service maps rather than alter your local /etc/services file.

Next, put a suitable line in the file /etc/inetd.conf (in the unlikely event that you are using a meta-daemon other than inetd, you are on your own). Note that the first item in this line matches the service name in /etc/services. Substitute appropriate values for your system in this line (see inetd (8)):

netbios-ssn stream tcp nowait root /usr/local/samba/bin/smbd -d1 -l/var/adm/smblogs/log -s/usr/local/samba/lib/smb.conf

(The above should appear in /etc/inetd.conf as a single line. Depending on your terminal characteristics, it may not appear that way in this man page. If the above appears as more than one line, please treat any newlines or indentation as a single space or TAB character.)

Note that there is no need to specify a port number here, even if you are using a non-standard port number.

Lastly, edit the configuration file to provide suitable services. To start with, the following two services should be all you need:

[homes]
  writeable = yes
[printers]
 writeable = no
 printable = yes
 path = /tmp
 public = yes

This will allow you to connect to your home directory and print to any printer supported by the host (user privileges permitting).

TESTING THE INSTALLATION

If running the server as a daemon, execute it before proceeding. If using a meta-daemon, either restart the system or kill and restart the meta-daemon. Some versions of inetd will reread their configuration tables if they receive a HUP signal.

If your machine's name is "fred" and your name is "mary", you should now be able to connect to the service \\fred\mary.

To properly test and experiment with the server, we recommend using the smbclient program (see smbclient (1)) and also going through the steps outlined in the file DIAGNOSIS.txt in the docs/ directory of your Samba installation.

VERSION

This man page is correct for version 2.0 of the Samba suite.

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 re-load its smb.conf configuration file within a short period of time.

To shut down a users 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 by sending it a SIGUSR1 (kill -USR1 <smbd-pid>) and lowered by sending it a SIGUSR2 (kill -USR2 <smbd-pid>). 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.

SEE ALSO

hosts_access (5), inetd (8), nmbd (8), smb.conf (5), smbclient (1), testparm (1), testprns (1), rpcclient (1), and the Internet RFC's rfc1001.txt, rfc1002.txt. In addition the CIFS (formerly SMB) specification is available as a link from the Web page : http://samba.org/cifs/.

AUTHOR

The original Samba software and related utilities were created by Andrew Tridgell samba-bugs@samba.org. Samba is now developed by the Samba Team as an Open Source project similar to the way the Linux kernel is developed.

The original Samba man pages were written by Karl Auer. The man page sources were converted to YODL format (another excellent piece of Open Source software, available at ftp://ftp.icce.rug.nl/pub/unix/) and updated for the Samba2.0 release by Jeremy Allison. samba-bugs@samba.org.

See samba (7) to find out how to get a full list of contributors and details on how to submit bug reports, comments etc.