Robert Eckstein, David Collier-Brown, Peter Kelly 1st Edition November 1999, 1-56592-449-5, 416 pages
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Chapter 9 |
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Samba is extremely robust. Once you've got everything set up the way you want, you'll probably forget that it is running. When trouble occurs, it's typically during installation or when you're trying to add something new to the server. Fortunately, there are a wide variety of resources that you can use to diagnose these troubles. While we can't describe in detail the solution to every problem that you might encounter, you should be able to get a good start at a resolution by following the advice given in this chapter.
The first section of the chapter lists the tool bag, a collection of tools available for troubleshooting Samba; the second section is a detailed how-to, and the last section lists extra resources you may need to track down particularly stubborn problems.
Sometimes Unix seems to be made up of a handful of applications and tools. There are tools to troubleshoot tools. And of course, there are several ways to accomplish the same task. When you are trying to solve a problem related to Samba, a good plan of attack is to check the following:
-
Samba logs -
Fault tree -
Unix utilities -
Samba test utilities -
Documentation and FAQs -
Searchable archives -
Samba newsgroups
Let's go over each of these one by one in the following sections.
Your first line of attack should always be to check the log files. The Samba log files can help diagnose the vast majority of the problems that beginning to intermediate Samba administrators are likely to face. Samba is quite flexible when it comes to logging. You can set up the server to log as little or as much as you want. Substitution variables that allow you to isolate individual logs for each machine, share, or combination thereof.
By default, logs are placed in
samba_directory
/var/smbd.log and
samba_directory
/var/nmbd.log, where
samba_directory is the location where Samba was installed (typically,
/usr/local/samba). As we mentioned in Chapter 4,
Disk Shares , you can override the location and name using the
log
file configuration option in
smb.conf. This option accepts all of the substitution variables mentioned in Chapter 2,
Installing Samba on a Unix System, so you could easily have the server keep a separate log for each connecting client by specifying the following in the
[global] section of
smb.conf :
log file = %m.log
Alternatively, you can specify a log directory to use with the
-l flag on the command line. For example:
smbd -l /usr/local/var/samba
Another useful trick is to have the server keep a log for each service (share) that is offered, especially if you suspect a particular share is causing trouble. Use the
%S variable to set this up in the
[global] section of the configuration file:
log file = %S.log
The level of logging that Samba uses can be set in the
smb.conf file using the global
log
level or
debug
level option; they are equivalent. The logging level is an integer which ranges from 0 (no logging), and increases the logging to voluminous by
log
level
=
3 . For example, let's assume that we are going to use a Windows client to browse a directory on a Samba server. For a small amount of log information, you can use
log
level
=
1 , which instructs Samba to show only cursory information, in this case only the connection itself:
105/25/98 22:02:11 server (192.168.236.86) connect to service public as user pcguest (uid=503,gid=100) (pid 3377)
Higher debug levels produce more detailed information. Usually you won't need any more than level 3; this is more than adequate for most Samba administrators. Levels above 3 are for use by the developers and dump enormous amounts of cryptic information.
Here is example output at levels 2 and 3 for the same operation. Don't worry if you don't understand the intricacies of an SMB connection; the point is simply to show you what types of information are shown at the different logging levels:
/* Level 2 */
Got SIGHUP
Processing section "[homes]"
Processing section "[public]"
Processing section "[temp]"
Allowed connection from 192.168.236.86 (192.168.236.86) to IPC$
Allowed connection from 192.168.236.86 (192.168.236.86) to IPC/
/* Level 3 */
05/25/98 22:15:09 Transaction 63 of length 67
switch message SMBtconX (pid 3377)
Allowed connection from 192.168.236.86 (192.168.236.86) to IPC$
ACCEPTED: guest account and guest ok
found free connection number 105
Connect path is /tmp
chdir to /tmp
chdir to /
05/25/98 22:15:09 server (192.168.236.86) connect to service IPC$ as user pcguest (uid=503,gid=100) (pid 3377)
05/25/98 22:15:09 tconX service=ipc$ user=pcguest cnum=105
05/25/98 22:15:09 Transaction 64 of length 99
switch message SMBtrans (pid 3377)
chdir to /tmp
trans <\PIPE\LANMAN> data=0 params=19 setup=0
Got API command 0 of form <WrLeh> <B13BWz> (tdscnt=0,tpscnt=19,mdrcnt=4096,mprcnt=8)
Doing RNetShareEnum
RNetShareEnum gave 4 entries of 4 (1 4096 126 4096)
05/25/98 22:15:11 Transaction 65 of length 99
switch message SMBtrans (pid 3377)
chdir to /
chdir to /tmp
trans <\PIPE\LANMAN> data=0 params=19 setup=0
Got API command 0 of form <WrLeh> <B13BWz> (tdscnt=0,tpscnt=19,mdrcnt=4096,mprcnt=8)
Doing RNetShareEnum
RNetShareEnum gave 4 entries of 4 (1 4096 126 4096)
05/25/98 22:15:11 Transaction 66 of length 95
switch message SMBtrans2 (pid 3377)
chdir to /
chdir to /pcdisk/public
call_trans2findfirst: dirtype = 0, maxentries = 6, close_after_first=0, close_if_end = 0 requires_resume_key = 0 level = 260, max_data_bytes = 2432
unix_clean_name [./DESKTOP.INI]
unix_clean_name [desktop.ini]
unix_clean_name [./]
creating new dirptr 1 for path ./, expect_close = 1
05/25/98 22:15:11 Transaction 67 of length 53
switch message SMBgetatr (pid 3377)
chdir to /
[...]
We cut off this listing after the first packet because it runs on for many pages. However, you should be aware that log levels above 3 will quickly fill your disk with megabytes of excruciating detail concerning Samba internal operations. Log level 3 is extremely useful for following exactly what the server is doing, and most of the time it will be obvious where an error is occurring by glancing through the log file.
A word of warning: using a high log level (3 or above) will
seriously slow down the Samba server. Remember that every log message generated causes a write to disk (an inherently slow operation) and log levels greater than 2 produce massive amounts of data. Essentially, you should turn on logging level 3 only when you're actively tracking a problem in the Samba server.
To turn logging on and off, set the appropriate level in the
[global] section of
smb.conf. Then, you can either restart Samba, or force the current daemon to reprocess the configuration file. You also can send the
smbd process a SIGUSR1 signal to increase its log level by one while it's running, and a SIGUSR2 signal to decrease it by one:
# Increase the logging level by 1
kill -SIGUSR1 1234
# Decrease the logging level by 1
kill -SIGUSR2 1234
An effective way to diagnose problems without hampering other users is to assign different log levels for different machines in
[global] section of the
smb.conf file. We can do this by building on the strategy we presented earlier:
[global]
log level = 0
log file = /usr/local/samba/lib/log.%m
include = /usr/local/samba/lib/smb.conf.%m
These options instruct Samba to use unique configuration and log files for each client that connects. Now all you have to do is create an
smb.conf file for a specific client machine with a
log
level
=
3 entry in it (the others will pick up the default log level of 0) and use that log file to track down the problem.
Similarly, if only particular users are experiencing a problem, and it travels from machine to machine with them, you can isolate logging to a specific user by adding the following to the
smb.conf file:
[global]
log level = 0
log file = /usr/local/samba/lib/log.%u
include = /usr/local/samba/lib/smb.conf.%u
Then you can create a unique
smb.conf file for each user (e.g.,
/usr/local/samba/lib/smb.conf.tim) files containing the configuration option
log
level
=
3 and only those users will get more detailed logging.
A rigorous set of tests that exercise the major parts of Samba are described in various files in the
/docs/textdocs directory of the Samba distribution kit, starting with
DIAGNOSIS.TXT. The fault tree in this chapter is a more detailed version of the basic tests suggested by the Samba team, but covers only installation and reconfiguration diagnosis, like
DIAGNOSIS.TXT. The other files in the
/docs subdirectoryies address specific problems (such as Windows NT clients) and instruct you how to troubleshoot items not included in this book. If the fault tree doesn't suffice, be sure to look at
DIAGNOSIS.TXT and its friends.
Sometimes it's useful to use a tool outside of the Samba suite to examine what's happening inside the server. Unix has always been a "kitchen-sink" operating system. Two diagnostic tools can be of particular help in debugging Samba troubles:
trace and
tcpdump.
The
trace command masquerades under several different names, depending on the operating system that you are using. On Linux it will be
strace, on Solaris you'll use
truss, and SGI will have
padc and
par. All have essentially the same function, which is to display each operating system function call as it is executed. This allows you to follow the execution of a program, such as the Samba server, and will often pinpoint the exact call that is causing the difficulty.
One problem that
trace can highlight is the location of an incorrect version of a dynamically linked library. This can happen if you've downloaded prebuilt binaries of Samba. You'll typically see the offending call at the end of the
trace, just before the program terminates.
A sample
strace output for the Linux operating system follows. This is a small section of a larger file created during the opening of a directory on the Samba server. Each line is a system-call name, and includes its parameters and the return value. If there was an error, the error value (e.g.,
ENOENT ) and its explanation are also shown. You can look up the parameter types and the errors that can occur in the appropriate
trace manual page for the operating system that you are using.
chdir("/pcdisk/public") = 0
stat("mini/desktop.ini", 0xbffff7ec) = -1 ENOENT (No such file or directory)
stat("mini", {st_mode=S_IFDIR|0755, st_size=1024, ...}) = 0
stat("mini/desktop.ini", 0xbffff7ec) = -1 ENOENT (No such file or directory)
open("mini", O_RDONLY) = 5
fcntl(5, F_SETFD, FD_CLOEXEC) = 0
fstat(5, {st_mode=S_IFDIR|0755, st_size=1024, ...}) = 0
lseek(5, 0, SEEK_CUR) = 0
SYS_141(0x5, 0xbfffdbbc, 0xedc, 0xbfffdbbc, 0x80ba708) = 196
lseek(5, 0, SEEK_CUR) = 1024
SYS_141(0x5, 0xbfffdbbc, 0xedc, 0xbfffdbbc, 0x80ba708) = 0
close(5) = 0
stat("mini/desktop.ini", 0xbffff86c) = -1 ENOENT (No such file or directory)
write(3, "\0\0\0#\377SMB\10\1\0\2\0\200\1\0"..., 39) = 39
SYS_142(0xff, 0xbffffc3c, 0, 0, 0xbffffc08) = 1
read(3, "\0\0\0?", 4) = 4
read(3, "\377SMBu\0\0\0\0\0\0\0\0\0\0\0\0"..., 63) = 63
time(NULL) = 896143871
This example shows several
stat calls failing to find the files they were expecting. You don't have to be a expert to see that the file
desktop.ini is missing from that directory. In fact, many difficult problems can be identified by looking for obvious, repeatable errors with
trace. Often, you need not look farther than the last message before a crash.
The
tcpdump program, written by Van Jacobson, Craig Leres, and Steven McCanne, and extended by Andrew Tridgell, allows you to monitor network traffic in real time. A variety of output formats are available and you can filter the output to look at only a particular type of traffic. The
tcpdump program lets you examine all conversations between client and server, including SMB and NMB broadcast messages. While its troubleshooting capabilities lie mainly at the OSI network layer, you can still use its output to get a general idea of what the server and client are attempting to accomplish.
A sample
tcpdump log follows. In this instance, the client has requested a directory listing and the server has responded appropriately, giving the directory names
homes ,
public ,
IPC$ , and
temp (we've added a few explanations on the right):
$
tcpdump -v -s 255 -i eth0 port not telnet
SMB PACKET: SMBtrans (REQUEST)
Request packet
SMB Command = 0x25
Request was ls or dir .
[000] 01 00 00 10 ....
>>> NBT Packet
Outer frame of SMB packe t
NBT Session Packet
Flags=0x0
Length=226
[lines skipped]
SMB PACKET: SMBtrans (REPLY)
Beginning of a reply to request
SMB Command = 0x25
Command was an ls or dir
Error class = 0x0
Error code = 0
No errors
Flags1 = 0x80
Flags2 = 0x1
Tree ID = 105
Proc ID = 6075
UID = 100
MID = 30337
Word Count = 10
TotParamCnt=8
TotDataCnt=163
Res1=0
ParamCnt=8
ParamOff=55
Res2=0
DataCnt=163
DataOff=63
Res3=0
Lsetup=0
Param Data: (8 bytes)
[000] 00 00 00 00 05 00 05 00 ........
Data Data: (135 bytes)
Actual directory contents:
[000] 68 6F 6D 65 73 00 00 00 00 00 00 00 00 00 00 00 homes... ........
[010] 64 00 00 00 70 75 62 6C 69 63 00 00 00 00 00 00 d...publ ic......
[020] 00 00 00 00 75 00 00 00 74 65 6D 70 00 00 00 00 ....u... temp....
[030] 00 00 00 00 00 00 00 00 76 00 00 00 49 50 43 24 ........ v...IPC$
[040] 00 00 00 00 00 00 00 00 00 00 03 00 77 00 00 00 ........ ....w...
[050] 64 6F 6E 68 61 6D 00 00 00 00 00 00 00 00 00 00 donham.. ........
[060] 92 00 00 00 48 6F 6D 65 20 44 69 72 65 63 74 6F ....Home Directo
[070] 72 69 65 73 00 00 00 49 50 43 20 53 65 72 76 69 ries...I PC Servi
[080] 63 65 20 28 53 61 6D ce (Sam
This is more of the same debugging session as with the
trace command; the listing of a directory. The options we used were
-v (verbose),
-i
eth0 to tell
tcpdump the interface to listen on (an Ethernet port), and
-s
255 to tell it to save the first 255 bytes of each packet instead of the default: the first 68. The option
port
not
telnet is used to avoid screens of telnet traffic, since we were logged in to the server remotely. The
tcpdump program actually has quite a number of options to filter just the traffic you want to look at. If you've used
snoop or
etherdump, they'll look vaguely familiar.
You can download the modified
tcpdump from the Samba FTP server at
ftp://samba.anu.edu.au/pub/samba/tcpdump-smb. Other versions don't include support for the SMB protocol; if you don't see output such as that shown in the example, you'll need to
use the SMB-enabled version.
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8.7 Backups with smbtar |
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9.2 The Fault Tree |
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