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Chapter 5. Unix Clients
In Chapter 3 we showed you how to configure Windows systems to access shared resources on both Windows and Samba servers. This has probably opened up a whole new world of computing for you—one in which you have to run to a Windows system every time you want to copy a file between Unix and Windows! In this chapter, we will show you the "other side"—how to access SMB shares from your favorite Unix system.
You can access SMB resources from Unix in three ways, depending on your version of Unix. A program included with the Samba distribution called smbclient can be used to connect with a share on the network in a manner similar to using ftp when transferring files to or from an FTP site.
If your system is running Linux, you can use the smbfs filesystem to mount SMB shares right onto your Linux filesystem, just as you would mount a disk partition or NFS filesystem. The SMB shares can then be accessed and manipulated by all programs running on the Linux system: command shells, desktop GUI interfaces, and application software.
For other Unix variants, smbsh can be run to enable common shell commands such as cd, ls, mv, wc, and grep to access and manipulate files and directories on SMB shares. This effectively extends the reach of the Unix shell and utilities beyond the Unix filesystem and into the SMB network.
All the Unix clients can access shares offered by either Windows systems or Samba servers. We have already shown you how to set up a share on a Samba server and could use that as an example to work with. But it's much more fun to use the Unix clients with shares served by Windows systems. So before we start covering the Unix clients in detail, we will take a quick detour and show you how to set up file shares on both Windows 95/98/Me and Windows NT/2000/XP systems.
When sharing files on Windows 95/98/Me, you can authenticate users in two different ways. Share-level security is the default and is easy to use. However, it is not as secure and can require users to type in passwords when connecting to shares. User-level security offers a better security model and can be used if you have either a Samba or Windows NT/2000 server on your network performing user authentication.
Click the "Share-level access control" or "User-level access control" radio button, depending on which you want to use. When using user-level access control, you will also need to fill in the name of your workgroup or Windows NT domain. Reboot as requested.
To share a folder, right-click the folder's icon and
select Sharing . . . . This will open the Sharing tab of the
folder's Properties dialog box. Click the
"Shared As:" radio button, and fill
in a name for the share (which defaults to the
folder's name) and a description, which will be
visible to client users. If you don't want the share
to be visible in the Network Neighborhood view of other Windows
clients, pick a name for the share that ends in a dollar sign
Figure 5-2 shows what the Sharing tab of the folder's Properties dialog box will look like when using share-level security. The security settings are very simple. You can select a radio button for read-only access or full (read/write) access, or have the user's permissions (either read-only or read/write) depend on which password they use. In accordance with which you select, you will be asked to assign either or both of the read-only and full-access passwords for the share.
If your system is configured with user-level security, the Sharing
tab of the folder's Properties dialog box will look
like Figure 5-3. As you can see,
we've created a share named
"DATA", and used the Add . . .
button to create permissions that allow read-only access for all
domain users and read/write (full access) for
When you are done specifying your settings for the share, click on the OK button, and the share will become available to users on network clients. Unless you chose a share name ending in a dollar sign, you can see it in the Network Neighborhood or My Network Places of Windows clients on the network. You can also now use the Unix clients described in this chapter to connect to the share.
To create a file share on Windows NT/2000/XP, you first must log in to the system as any member of the Administrators, Power Users, or Server Operators groups. Right-click the icon of a folder you wish to share, and click Sharing . . . in the pop-up menu. The Sharing tab of the folder's Properties dialog box will appear, as shown in Figure 5-4. Click the "Share this folder" radio button.
Share name: will default to the name of the folder, and you can
change it if you want. One reason you might want to use a different
name for the share is to make the share not appear in browse lists
(as displayed by the Network Neighborhood, for example). This can be
done by using a share name ending in a dollar sign
$). You can also add a description of the share
in the Comment: text area. The description will appear to users of
network clients and can help them understand the contents of the
By clicking the Permissions button, you can set permissions for the share on a user-by-user basis. This is equivalent to the user-level security of Windows 95/98/Me file sharing. On Windows NT/2000/XP, Microsoft recommends that share permissions be set to allow full access by everyone, with the permissions controlled on a file-by-file basis using filesystem access control lists (ACLs). The actual permissions given to network clients are a combination of the share permissions and file access permissions. To edit the ACL for the folder, click the Security tab. For more information on ACLs, see Section 8.3 in Chapter 8.
If you want, you can limit the number of users who can concurrently connect to the share using the "User limit:" radio button. The New Share button allows you to create multiple file shares for the same folder, each having its own name, comment, user limit, and other parameters.
When you are done, click the OK button, and the folder will be accessible from clients on the network.
The Samba Team supplies smbclient as a basic part of the Samba suite. At
first, it might seem to be a primitive interface to the SMB network,
but smbclient is actually a versatile tool. It
can be used for browsing shares on servers, testing configurations,
debugging, accessing shared printers, backing up shared data, and
automating administrative tasks in shell scripts. And unlike
smbfs and smbsh,
smbclient works on all Unix variants that
In this chapter we'll focus mostly on running smbclient as an interactive shell, using its ftp-like commands to access shared directories on the network. Using smbclient to access printers and perform backups will be covered in Chapter 10.
A complete reference to smbclient is found in Appendix C.
The -L option can be used with smbclient to list the resources on a single computer. Assuming the Samba server is configured to take the role of the master browser, we can obtain a list of the computers in the domain or workgroup like this:
smbclient -L toltecadded interface ip=172.16.1.1 bcast=172.16.1.255 nmask=255.255.255.0 Password: Domain=[METRAN] OS=[Unix] Server=[Samba 2.2.5] Sharename Type Comment --------- ---- ------- test Disk For testing only, please IPC$ IPC IPC Service (Samba 2.2.5) ADMIN$ Disk IPC Service (Samba 2.2.5) Server Comment --------- ------- MAYA Windows 98 MIXTEC Samba 2.2.5 TOLTEC Samba 2.2.5 ZAPOTEC Workgroup Master --------- ------- METRAN TOLTEC
In the column labeled "Server",
zapotec are shown along with toltec, the Samba
server. The services on
toltec are listed under
"Sharename". The IPC$ and ADMIN$
shares are standard Windows services that are used for network
communication and administrative purposes, and
test is the directory we added as a share in
Now that we know the names of computers in the domain, we can list
services on any of those computers. For example, here is how we would
list the services offered by
maya, a Windows 98
smbclient -L mayaadded interface ip=172.16.1.1 bcast=172.16.1.255 nmask=255.255.255.0 Password: Sharename Type Comment --------- ---- ------- PRINTER$ Disk HP Printer HP 932C on Maya D Disk D: on Maya E Disk E: on Maya ADMIN$ Disk IPC$ IPC Remote Inter Process Communication Server Comment --------- ------- Workgroup Master --------- -------
A shared printer is attached to
maya, so we see
the PRINTER$ administrative service, along with the HP share for the
printer itself. Also on
maya are the D and E
shares, which allow access across the network to
maya's D: and E: drives. It is
normal for the Server and Workgroup sections to be empty when listing
services on a Windows client.
As with any other SMB client, smbclient needs to supply a username and password if it is authenticating in a domain environment or if it is contacting a Samba server that is set up with user-level security. In a workgroup environment, it will at least need a password to use when connecting with a password-protected resource.
This method is useful if you are logged in to the system under an account that is not Samba-enabled or you are testing your configuration to see how it treats another user. With either method, you can avoid having to enter the username and/or password each time you run smbclient by creating an alias for the command or creating a shell function or shell script. For example, with the bash shell, it is possible to define a function like this:
Another method that can be used to supply both the username and password is to set the USER and PASSWD environment variables. Either set the USER environment variable using the username%password format, or set the USER environment variable to the username, and set PASSWD to the user's password.
If security is a concern, you definitely should avoid providing your password on the command line because it is very easy for "shoulder surfers" to obtain, as well as anyone who looks through your shell's command history.
If you keep your Samba password in a credentials file, shell startup file, or shell script, make sure the file's permissions prohibit other users from reading or writing it. (Use an octal permissions mode of 0600.) Security experts never keep passwords in files owned by nonroot users or accessible by anyone other than the superuser. As part of their security policy, some organizations do not permit passwords to be stored in files, so you might want to check first before using this method.
The authentication method that uses the USER and PASSWD environment variables isn't any more secure. Environment variables are usually set either on the command line or in one or more of the shell's startup files, so this method suffers from the same weaknesses we've just discussed. In addition, any program run by the user has access to the shell's environment variables, making a Trojan horse attack on the PASSWD variable really easy!
A common use for smbclient is to use it as an ftp-like shell to access SMB resources on the network. To begin a session, smbclient must be provided with the UNC of a resource (which you can find using the -L option) on the command line, like this:
Forward slashes are accepted by smbclient for
the share's UNC, which makes entering the UNC on the
command line easier. Backslashes can also be used, but they must be
quoted or escaped, and it is somewhat more difficult to type
After connecting to the share, smbclient
smb: \> prompt, waiting for a
command to be entered. Commands are similar to those with which you
might be familiar in ftp and are also somewhat
similar to Unix shell commands. To get a list of
smbclient commands, use the
Some commands in the previous list are synonyms for other commands. For example, the ? command is a synonym for help. You can give this command the name of another command as an argument to get a concise reminder of what the command does and how to use it:
lists all files ending in "doc" in the current directory on the remote system. In the listing, the leftmost column shows the filename. Moving left to right, we see the file's MS-DOS attributes, then its size, and the time it was last modified.
As with any other Unix utility, smbclient has a working directory on the local host. It also has another current directory on the remote SMB share. With smbclient, the cd command is used to move around on the remote system:
Most of smbclient's commands
are for performing operations on remote files and directories. There
is no command for listing the contents of the local directory.
However, smbclient allows a shell escape. Any
command preceded by an exclamation point (
interpreted as a shell command and is run in a subshell on the local
system. For example:
lists the contents of /u/snd. By using smbclient's commands to operate on the remote system—and shell-escaped commands to operate on the local system—it is possible to manipulate data on both systems without having to exit smbclient or open another shell window.
File transfer is performed using the get and put commands. The get command transfers a single file from the remote to the local system, and the put command copies a file from the local to the remote system. For example, the following command copies the file readme.txt to the SMB share:
Unlike ftp, smbclient does not have ascii and binary commands to set the type of the file that is being transferred. Before transferring a text file from a Unix system to a Windows or Macintosh system, you might want to use the GNU unix2dos command to reformat newlines in the file to work with the carriage return linefeed (CRLF) standard:
To transfer more than one file with a single command, you can use the mget and mput commands, which accept a list of filenames in the command line. The list can be provided by typing in the filenames on the command line separated by spaces, or the group of files can be specified with a pattern as one would use in Unix shell commands. The command:
By default, if you specify the name of a directory, smbclient will not copy the contents of the directory. To transfer the entire contents of directories listed in the mput or mget command, you must first use the recurse command:
mget accgetting file tomm.wav of size 55494 as tomm.wav (2580.6 kb/s) (average 2087.3 kb/s) getting file toml.wav of size 57220 as toml.wav (2660.9 kb/s) (average 2167.6 kb/s) getting file tomh.wav of size 55936 as tomh.wav (2601.2 kb/s) (average 2220.8 kb/s) getting file snare.wav of size 22132 as snare.wav (1200.7 kb/s) (average 2123.7 kb/s) getting file rim.wav of size 8314 as rim.wav (1623.8 kb/s) (average 2110.8 kb/s) getting file handclap.wav of size 14180 as handclap.wav (1978.2 kb/s) (average 2106.2 kb/s) getting file bassdrum.wav of size 6950 as bassdrum.wav (2262.3 kb/s) (average 2108.5 kb/s)
Directory recursion applies to all commands, so if an ls command is used while directory recursion is on, all files in the directory tree are listed. To turn directory recursion off again, simply re-enter the command. At the same time, you might also wish to toggle prompting back to its initial state:
There are other smbclient commands that you might find useful. The mkdir command can be used to create a directory; rmdir removes a directory; rm deletes a file; and rename changes a file's name. These behave very similarly to their Unix shell counterparts. Appendix C contains a complete reference to smbclient and its command set.
To exit smbclient, use the exit or quit command:
Everything that smbclient needs to know to perform the operation has been specified in the command. There is no interactive session, so a command such as this can be placed inside a shell script or a program in some other programming language.
By using smbclient in this manner, it is possible to create customized commands using shell functions, scripts or aliases. For example, suppose we wanted a command to print a short listing of files in a shared directory, showing just the names of the files. Using a bash function, we could define a command smbls as follows:
Another use for smbclient in scripts is performing administrative tasks. Suppose a group of users on Windows clients are sharing a set of files as part of a project on which they are working. Instead of expecting them to coordinate making daily backups, we could write a script that copies the share to the Samba server and run the script nightly as a cron job. The directory on the Samba server could be shared as well, allowing any of the users to retrieve a backup file on their own, without having to bother an administrator.
A major use of smbclient is to create and restore backups of SMB file shares. The backup files smbclient writes are in tar format, making them easy to work with and portable among all Unix versions. Using smbclient on a Unix server to run network backups can result in a more centralized and easily managed solution for providing data integrity because both SMB shares and NFS filesystems can be backed up on the same system.
This causes smbclient to change its working directory to the trans directory of the \\maya\e share before starting the backup. It is also possible to use smbclient's tar command in interactive mode, like this:
With the previous code, only the trans subdirectory in the \\maya\e share will be backed up, using the settings specified in the tarmode command. To have this type of backup run automatically from a script, use the -c option:
Using either the -T command-line option or smbclient's tar command, additional options can be supplied. It is necessary to specify either the c option to create a backup archive or the x option to extract (restore) one.
The other options can be appended to the option string and are explained in the section on smbclient in Appendix C. They allow you to create incremental backups, specify which files to include or exclude from the backup, and specify a few other miscellaneous settings. For example, suppose we wish to create an incremental backup of a share and reset the archive bit on the files to set things up for the next incremental backup. Instead of using the interactive commands:
tarmode inc reset quietsmb: \>
tar c backup.tar
we could either use the interactive command:
tar cgaq backup.tar
or specify the -Tcgaq option on the smbclient command line.
Your best strategy for using smbclient for network backups depends on your local configuration. If you have only a few Windows systems sharing a small amount of data, you might create a script containing smbclient -Tc commands to back up each share to a separate tar file, placing the files in a directory that is included with regular backups of the Unix system. If you have huge SMB shares on your network, you might prefer to write the backup directly to a tape drive. You can do this with smbclient just as you would with a Unix tar command:
smbclient //maya/d -A samba-domain-pw -Tc >/dev/tape
After you have become more familiar with smbclient and have an automated backup system in place, you might find that using Samba has dramatically decreased your anxiety regarding the integrity of your network's data. The authors of this book are experienced Unix system administrators, and we highly recommend having a backup strategy that has been carefully planned, implemented, and most importantly, tested and known to work as it is supposed to.
On Linux, the smbfs filesystem can be used to mount SMB shares onto the Linux filesystem in a manner similar to mounting disk partitions on NFS filesystems. The result is so transparent that users on the Linux system might never be aware that they are accessing files through a Windows or Samba server. Files and directories appear as any other files or directories on the local Linux system, although there are a few differences in behavior relating to ownership and permissions.
Although smbfs is based on the Samba code, it is not itself part of the Samba distribution. Instead, it is included with Linux as a standard part of the Linux filesystem support.
The smbmount and
smbmnt programs are part of the Samba
distribution and are needed on the client to mount smbfs filesystems.
Samba must be compiled with the
configure option to make sure these programs are compiled. They refer
to smb.conf for information they need regarding
the local system and network configuration, so you will need a
file on the system, even if it is not acting as a Samba server.
Replace Share-UNC with the UNC for the SMB share, and mount-point with the full path to the directory in the Linux filesystem to use as the mount point. The options argument is used to set the exact manner in which the share is mounted. Let's look at an example of a smbmount command:
The argument to the -o option might look a
little complex. It is a comma-separated list of
credentials key is set to the name of
the credentials file, which is used to give
smbmount a valid username and password with
which to authenticate while connecting to the share. The format is
identical to that used by smbclient (as
explained in the previous section), so you can use the same
credentials file for both clients. If you want, you can use the
to specify the username and password directly in the
smbmount command, although this is considerably
The smbmount command accepts the same authentication methods as smbclient. The comments in the section on smbclient regarding supplying passwords on the command line—and keeping passwords in files and environment variables—also apply here.
The rest of the options tell smbmount how to translate between the SMB filesystem and the Unix filesystem, which differ in their handling of ownership and permissions. The uid and gid options specify the owner and group to be assigned to all directories and files in the mounted share.
The fmask and dmask options specify bitmasks for permissions of files and directories, respectively. These bitmasks are logically ANDed with whatever permissions are granted by the server to create the effective permissions on the client Unix system. On the server side, the permissions granted depend on the server's operating system. For a Windows 95/98/Me server using share-mode security, the MS-DOS read-only attribute can be set on individual files and directories and combined with the Full Access or Read Only permissions on the share as a whole. In user-level security mode, Windows 95/98/Me can have ACL-like permissions applied to the entire share, as discussed in Chapter 4. Windows NT/2000/XP support ACLs on individual files and directories, with Full Control, Change, or Read permissions that can be applied to the entire share. If the server is a Samba server, the permissions are whatever is defined by the Samba share and the local Unix system for the individual files and directories. In every case, the permissions applied to the share act to further limit access, beyond what is specified for the individual files and directories.
You might think that the fmask and dmask permission masks can be used only to reduce the effective permissions on files and directories, but this is not always the case. For example, suppose that a file is being shared by a Windows 95/98/Me server using share-mode security and that some number of users have been given the Full Access password for the share. If the share is mounted with smbmount using an fmask of 666, read/write permissions are granted on the Unix system not only for the owner, but for everyone else on the Unix system as well!
cd /smb/e ; ls -ltotal 47 drwxrwxr-x 1 jay jay 512 Jan 8 20:21 CD-images drwxrwxr-x 1 jay jay 512 Jan 6 21:50 lectures -rw-rw-r-- 1 jay jay 131 Dec 18 09:12 ms-ProfPol-wp.doc -rw-rw-r-- 1 jay jay 59 Dec 18 09:12 profile-map -rw-rw-r-- 1 jay jay 131 Jan 15 05:01 readme.txt drwxrwxr-x 1 jay jay 512 Feb 4 2002 RECYCLED -rw-rw-r-- 1 jay jay 33969 Dec 10 20:22 smbclient.doc -rw-rw-r-- 1 jay jay 7759 Dec 10 20:20 smbmount.doc -rw-rw-r-- 1 jay jay 1914 Dec 10 20:17 smbsh.txt drwxrwxr-x 1 jay jay 512 Jan 10 03:54 trans
For the most part, the files and directories contained in the mounted smbfs filesystem will work just like any others, except for limitations imposed by the nature of SMB networking. For example, not even the superuser can perform the operation:
Aside from little things such as these, the mounted smbfs filesystem can be used in conjunction with virtually any application, and you might be pleasantly surprised at how nicely it integrates with your Linux-based computing environment. You can even create symbolic links in the Unix filesystem, pointing to files and directories inside SMB shares. However, unless the server is a Samba server that supports Unix CIFS extensions, you will not be able to create a symbolic link inside the mounted smbfs filesystem.
Replace Share-UNC with the UNC of the share (using the forward slash format), and replace mount-point with the name of the directory in the Linux filesystem on which the share will be mounted. In place of options, simply use the string that you used with the -o flag in the smbmount command.
Once you have found the arguments to use with the smbmount command to mount the share the way you like it, it is a very simple matter to create the entry for /etc/fstab. The smbmount command we used to mount the share \\maya\e on /smb/e would translate to this /etc/fstab entry: