Chapter 5. Unix Clients

Listing Services

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 toltec
added 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", maya, mixtec, and 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 Chapter 2.

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 workstation:

$ smbclient -L maya
added 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.

Authenticating with smbclient

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.

By default, smbclient uses the username of the user who runs it and then prompts for a password. If you are using smbclient a lot, you might tire of entering your password every time.

smbclient supports some alternate methods of entering a username and password. The password can be entered on the command line, like this:

$ smbclient //maya/e jayspassword

Or both the username and password can be supplied by using the -U option, including the username and password separated by a percent (%) character:

$ smbclient //maya/e -U kelly%kellyspassword

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:

smbcl(  )
{
    smbclient $* -U jay%jayspassword
}

Adding the definition to the shell's startup script (which would be ~/.bash_profile for bash) would result in the definition affecting all subsequent shell invocations.

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.

It is also possible to create a credentials file containing the username on the first line and the password on the second line, like this:

username = jay
password = jayspassword

Then, smbclient is run using the -A option to specify the name of the file:

$ smbclient //maya/e -A ~/.smbpw

NOTE

Of the methods we described in this section, the only one that is really secure is the default method of allowing smbclient to prompt for the password and typing in the password without echoing.

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!

An Interactive smbclient Session

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:

$ smbclient //maya/e
added interface ip=172.16.1.3 bcast=172.16.1.255 nmask=255.255.255.0
Password: 
smb: \>

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 '\\maya\e' or \\\\maya\\e. After connecting to the share, smbclient displays the 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 help command:

smb: \> help
ls             dir            du             lcd            cd             
pwd            get            mget           put            mput           
rename         more           mask           del            open           
rm             mkdir          md             rmdir          rd             
prompt         recurse        translate      lowercase      print          
printmode      queue          cancel         quit           q              
exit           newer          archive        tar            blocksize      
tarmode        setmode        help           ?              history        
!

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:

smb: \> ? ls
HELP ls:
        <mask> list the contents of the current directory

The term <mask> refers to a file-matching pattern as commonly found in Unix shells and utilities. For example:

smb: \> ls *doc
  ms-ProfPol-wp.doc                   A      131  Tue Dec 18 09:12:34 2002
  smbclient.doc                       A    33969  Mon Dec 10 20:22:24 2002
  smbmount.doc                        A     7759  Mon Dec 10 20:20:00 2002

                      48590 blocks of size 524288. 40443 blocks available

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:

smb: \> cd trans   
smb: \trans\>

Notice how the prompt changes to reflect the new current working directory. To change your current directory on the local system, use the lcd command:

smb: \trans\> lcd /u/snd
the local directory is now /u/snd

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 (!) is interpreted as a shell command and is run in a subshell on the local system. For example:

smb: \trans\> ! ls -l
total 16
drwxrwxr-x    2 jay      jay          4096 Jan 10 14:46 dr220-fet
drwxrwxr-x    2 jay      jay          4096 Sep 22 12:16 dr220-tube
-rw-rw-r--    1 jay      jay           131 Jan 10 02:22 readme.txt
drwxrwxr-x    7 jay      jay          4096 Jan 10 02:19 xl1

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:

smb: \trans\> put readme.txt
putting file readme.txt as \trans\readme.txt (127.9 kb/s) (average 10.7 kb/s)

NOTE

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:

$ unix2dos text_file >text_file.txt

and then transfer the CRLF-formatted version. After transferring a text file from a Windows or Macintosh system to Unix, you can use the GNU dos2unix command to perform the inverse operation:

$ dos2unix text_file.txt >text_file

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:

smb: \trans\> mget plain/*

copies all the files in the directory plain on the SMB share to the current directory on the local system. By default, smbclient prompts for each file, asking if you want to copy it:

smb: \trans\> mget plain/*
Get file tomm.wav? n
Get file toml.wav? n
Get file tomh.wav? n
Get file snare.wav? n
Get file rim.wav? n
Get file handclap.wav? n
Get file bassdrum.wav? n

If you are sure you want to copy all the files, you can turn off prompting with the prompt command, like this:

smb: \trans\> prompt
prompting is now off

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:

smb: \trans\> recurse
directory recursion is now on

After setting things up with the prompt and recurse commands, we can copy a directory like this:

smb: \trans\> mget acc
getting 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:

smb: \trans\> recurse
directory recursion is now off
smb: \trans\> prompt
prompting is now on

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:

smb: \trans\> quit 

Programming with smbclient

The -c option of smbclient allows a list of commands to be passed on the command line. To copy the file \\maya\e\trans\readme.txt to /u/snd/readme.txt, we might use the command:

$ smbclient //maya/e -c "lcd /u/snd; cd trans; get readme.txt" -A ~/.smbpw

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:

smbls(  )
{
        share=`echo $1 | cut -d '/' -f '1-4'`
        dir=`echo $1 | cut -d '/' -f '5-'`
        smbclient $share -c "cd $dir; ls" -A ~/.smbpw | \
                        grep "^  " | cut -d ' ' -f 3 - | sort
}

After defining this function, we can use smbls like this:

$ smbls //maya/e
CD-images
lectures
ms-ProfPol-wp.doc
profile-map
readme.txt
RECYCLED
smbclient.doc
smbmount.doc
smbsh.txt
trans
$ smbls //maya/e/lectures
.
..
lecture1.mp3
lecture2.mp3
lecture3.mp3
lecture4.mp3
lecture5.mp3
lecture6.mp3
lecture7.mp3
lecture8.mp3
lecture9.mp3

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.

Backups with smbclient

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.

You can use smbclient to perform backups in two ways. When backing up an entire share, the simplest method is to use the -Tc option on the command line:

# smbclient //maya/e -A samba-domain-pw -Tc >maya-e.tar

This will create a tar archive of the \\maya\e share in the file maya-e.tar. By using the -D option, it is possible to back up a directory in the share, rather than the whole share:

# smbclient //maya/e -A samba-domain-pw -D trans -Tc >maya-e.tar

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:

# smbclient //maya/e 
added interface ip=172.16.1.3 bcast=172.16.1.255 nmask=255.255.255.0
Password:
smb: \> cd trans
smb: \trans\> tarmode full hidden system quiet
smb: \trans\> tar c maya-e-trans.tar

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:

# smbclient //maya/e -A samba-domain-pw -c "cd trans; tarmode full hidden \
    system quiet; tar >maya-e-trans.tar"

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.[1]

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:

smb: \> tarmode inc reset quiet
smb: \> tar c backup.tar

we could either use the interactive command:

smb: \> 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.

Mounting an smbfs Filesystem

The smbmount command is used to mount an smbfs filesystem into the Linux filesystem. The basic usage is:

# smbmount Share-UNC mount-point -o options

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:

# smbmount //maya/e /smb/e \
    -o "credentials=/home/jay/.smbpw,uid=jay,gid=jay,fmask=664,dmask=775"

Here we are mounting share \\maya\e from a Windows 98 system on the mount point /smb/e on the Linux system.

NOTE

If your Linux kernel doesn't include smbfs support, you will get the error message:

ERROR: smbfs filesystem not supported by the kernel

In this case, you must configure and compile a new kernel to include support for smbfs. When smbfs is installed, and an SMB share is mounted, you can run the command:

$ cat /proc/filesystems

and see a line that looks like:

nodev   smbfs

in the command's output.

The mount point must exist before smbmount is run and can be created using the mkdir command:

# mkdir /smb/e

The argument to the -o option might look a little complex. It is a comma-separated list of key=value pairs. The 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 key=value pair username=name%password to specify the username and password directly in the smbmount command, although this is considerably less secure.

TIP

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.

TIP

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!

After mounting the \\maya\d share to /smb/e, here is what the contents of /smb/e look like:

$ cd /smb/e ; ls -l
total 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:

# chown root lectures
chown: changing ownership of 'lectures': Operation not permitted

because SMB shares do not intrinsically support the idea of ownership. Some odd behaviors can result from this. For example, the command:

# chmod 777 readme.txt

does not produce an error message, although nothing has been changed. The file readme.txt still has permissions set to 664:

# ls -l readme.txt
-rw-rw-r--    1 jay      jay           131 Jan 15 05:01 readme.txt

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.

Mounting smbfs Filesystems Automatically

As with other types of filesystems, an smbfs filesystem can be mounted automatically during system bootup by creating an entry for it in /etc/fstab. The format for the entry is as follows:

Share-UNC mount-point  smbfs  options 0 0

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:

//maya/e /smb/e  smbfs  
credentials=/home/jay/.smbpw,uid=jay,gid=jay,fmask=664,dmask=775 0 0

(Please note that this should all go on one line.)

WARNING

If you make a mistake in modifying /etc/fstab, your system might not reboot properly, and you might be forced to boot into single-user mode to fix the problem. Before you edit /etc/fstab, be sure to make a backup copy of it, and be prepared to recover your system if anything