Previous Next Table of Contents

11. Troubleshooting

11.1 Why am I getting ``Proxy Access Denied?''

If squid is in httpd-accelerator mode, it will accept normal HTTP requests and forward them to a HTTP server, but it will not honor proxy requests. If you want your cache to also accept proxy-HTTP requests then you must enable this feature:

        http_accel_with_proxy on
Alternately, you may have misconfigured one of your ACLs. Check the access.log and squid.conf files for clues.

11.2 I can't get local_domain to work; Squid is caching the objects from my local servers.

The local_domain directive does not prevent local objects from being cached. It prevents the use of sibling caches when fetching local objects. If you want to prevent objects from being cached, use the cache_stoplist or http_stop configuration options (depending on your version).

11.3 I get Connection Refused when the cache tries to retrieve an object located on a sibling, even though the sibling thinks it delivered the object to my cache.

If the HTTP port number is wrong but the ICP port is correct you will send ICP queries correctly and the ICP replies will fool your cache into thinking the configuration is correct but large objects will fail since you don't have the correct HTTP port for the sibling in your squid.conf file. If your sibling changed their http_port, you could have this problem for some time before noticing.

11.4 Running out of filedescriptors

If you see the Too many open files error message, you are most likely running out of file descriptors. This may be due to running Squid on an operating system with a low filedescriptor limit. This limit is often configurable in the kernel or with other system tuning tools. There are two ways to run out of file descriptors: first, you can hit the per-process limit on file descriptors. Second, you can hit the system limit on total file descriptors for all processes.

Linux

Have a look at filehandle.patch by Michael O'Reilly

If your kernel version is 2.2.x or greater, you can read and write the maximum number of file handles and/or inodes simply by accessing the special files:

        /proc/sys/fs/file-max
        /proc/sys/fs/inode-max
So, to increase your file descriptor limit:
        echo 3072 > /proc/sys/fs/file-max

If your kernel version is between 2.0.35 and 2.1.x (?), you can read and write the maximum number of file handles and/or inodes simply by accessing the special files:

        /proc/sys/kernel/file-max
        /proc/sys/kernel/inode-max

While this does increase the current number of file descriptors, Squid's configure script probably won't figure out the new value unless you also update the include files, specifically the value of OPEN_MAX in /usr/include/linux/limits.h.

Solaris

Add the following to your /etc/system file to increase your maximum file descriptors per process:

        set rlim_fd_max = 4096
        set rlim_fd_cur = 1024

You should also #define SQUID_FD_SETSIZE in include/config.h to whatever you set rlim_fd_max to. Going beyond 4096 may break things in the kernel.

Solaris' select(2) only handles 1024 descriptors, so if you need more, edit src/Makefile and enable $(USE_POLL_OPT). Then recompile squid. (version 1.1 only, version 2 automatically uses poll() on Solaris).

FreeBSD

by Torsten Sturm

  1. How do I check my maximum filedescriptors?

    Do sysctl -a and look for the value of kern.maxfilesperproc.

  2. How do I increase them?
            sysctl -w kern.maxfiles=XXXX
            sysctl -w kern.maxfilesperproc=XXXX
    
    Warning: You probably want maxfiles > maxfilesperproc if you're going to be pushing the limit.
  3. What is the upper limit?

    I don't think there is a formal upper limit inside the kernel. All the data structures are dynamically allocated. In practice there might be unintended metaphenomena (kernel spending too much time searching tables, for example).

General BSD

For most BSD-derived systems (SunOS, 4.4BSD, OpenBSD, FreeBSD, NetBSD, BSD/OS, 386BSD, Ultrix) you can also use the ``brute force'' method to increase these values in the kernel (requires a kernel rebuild):

  1. How do I check my maximum filedescriptors?

    Do pstat -T and look for the files value, typically expressed as the ratio of currentmaximum/.

  2. How do I increase them the easy way?

    One way is to increase the value of the maxusers variable in the kernel configuration file and build a new kernel. This method is quick and easy but also has the effect of increasing a wide variety of other variables that you may not need or want increased.

  3. Is there a more precise method?

    Another way is to find the param.c file in your kernel build area and change the arithmetic behind the relationship between maxusers and the maximum number of open files.

Here are a few examples which should lead you in the right direction:
  1. SunOS

    Change the value of nfile in usr/kvm/sys/conf.common/param.c/tt> by altering this equation:

            int     nfile = 16 * (NPROC + 16 + MAXUSERS) / 10 + 64;
    
    Where NPROC is defined by:
            #define NPROC (10 + 16 * MAXUSERS)
    

  2. FreeBSD (from the 2.1.6 kernel)

    Very similar to SunOS, edit /usr/src/sys/conf/param.c and alter the relationship between maxusers and the maxfiles and maxfilesperproc variables:

            int     maxfiles = NPROC*2;
            int     maxfilesperproc = NPROC*2;
    
    Where NPROC is defined by: #define NPROC (20 + 16 * MAXUSERS) The per-process limit can also be adjusted directly in the kernel configuration file with the following directive: options OPEN_MAX=128

  3. BSD/OS (from the 2.1 kernel)

    Edit /usr/src/sys/conf/param.c and adjust the maxfiles math here:

            int     maxfiles = 3 * (NPROC + MAXUSERS) + 80;
    
    Where NPROC is defined by: #define NPROC (20 + 16 * MAXUSERS) You should also set the OPEN_MAX value in your kernel configuration file to change the per-process limit.

Reconfigure afterwards

NOTE: After you rebuild/reconfigure your kernel with more filedescriptors, you must then recompile Squid. Squid's configure script determines how many filedescriptors are available, so you must make sure the configure script runs again as well. For example:

    cd squid-1.1.x
        make realclean
        ./configure --prefix=/usr/local/squid
        make

11.5 What are these strange lines about removing objects?

For example:

        97/01/23 22:31:10| Removed 1 of 9 objects from bucket 3913
        97/01/23 22:33:10| Removed 1 of 5 objects from bucket 4315
        97/01/23 22:35:40| Removed 1 of 14 objects from bucket 6391

These log entries are normal, and do not indicate that squid has reached cache_swap_high.

Consult your cache information page in cachemgr.cgi for a line like this:

       Storage LRU Expiration Age:     364.01 days

Objects which have not been used for that amount of time are removed as a part of the regular maintenance. You can set an upper limit on the LRU Expiration Age value with reference_age in the config file.

11.6 Can I change a Windows NT FTP server to list directories in Unix format?

Why, yes you can! Select the following menus:

This will bring up a box with icons for your various services. One of them should be a little ftp ``folder.'' Double click on this.

You will then have to select the server (there should only be one) Select that and then choose ``Properties'' from the menu and choose the ``directories'' tab along the top.

There will be an option at the bottom saying ``Directory listing style.'' Choose the ``Unix'' type, not the ``MS-DOS'' type.

--Oskar Pearson <oskar@is.co.za>

11.7 Why am I getting ``Ignoring MISS from non-peer x.x.x.x?''

You are receiving ICP MISSes (via UDP) from a parent or sibling cache whose IP address your cache does not know about. This may happen in two situations.

  1. If the peer is multihomed, it is sending packets out an interface which is not advertised in the DNS. Unfortunately, this is a configuration problem at the peer site. You can tell them to either add the IP address interface to their DNS, or use Squid's 'udp_outgoing_address' option to force the replies out a specific interface. For example:

    on your parent squid.conf:

            udp_outgoing_address proxy.parent.com
    
    on your squid.conf:
            cache_host proxy.parent.com parent 3128 3130
    

  2. You can also see this warning when sending ICP queries to multicast addresses. For security reasons, Squid requires your configuration to list all other caches listening on the multicast group address. If an unknown cache listens to that address and sends replies, your cache will log the warning message. To fix this situation, either tell the unknown cache to stop listening on the multicast address, or if they are legitimate, add them to your configuration file.

11.8 DNS lookups for domain names with underscores (_) always fail.

The standards for naming hosts ( RFC 952, RFC 1101) do not allow underscores in domain names:

A "name" (Net, Host, Gateway, or Domain name) is a text string up to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus sign (-), and period (.).
The resolver library that ships with recent versions of BIND enforces this restriction, returning an error for any host with underscore in the hostname. The best solution is to complain to the hostmaster of the offending site, and ask them to rename their host.

Some people have noticed that RFC 1033 implies that underscores are allowed. However, this is an informational RFC with a poorly chosen example, and not a standard by any means.

11.9 Why does Squid say: ``Illegal character in hostname; underscores are not allowed?'

See the above question. The underscore character is not valid for hostnames.

Some DNS resolvers allow the underscore, so yes, the hostname might work fine when you don't use Squid.

To make Squid allow underscores in hostnames, add this line to src/squid.h:

        #define ALLOW_HOSTNAME_UNDERSCORES 1
and then recompile.

11.10 Why am I getting access denied from a sibling cache?

The answer to this is somewhat complicated, so please hold on. NOTE: most of this text is taken from ICP and the Squid Web Cache.

An ICP query does not include any parent or sibling designation, so the receiver really has no indication of how the peer cache is configured to use it. This issue becomes important when a cache is willing to serve cache hits to anyone, but only handle cache misses for its paying users or customers. In other words, whether or not to allow the request depends on if the result is a hit or a miss. To accomplish this, Squid acquired the miss_access feature in October of 1996.

The necessity of ``miss access'' makes life a little bit complicated, and not only because it was awkward to implement. Miss access means that the ICP query reply must be an extremely accurate prediction of the result of a subsequent HTTP request. Ascertaining this result is actually very hard, if not impossible to do, since the ICP request cannot convey the full HTTP request. Additionally, there are more types of HTTP request results than there are for ICP. The ICP query reply will either be a hit or miss. However, the HTTP request might result in a ``304 Not Modified'' reply sent from the origin server. Such a reply is not strictly a hit since the peer needed to forward a conditional request to the source. At the same time, its not strictly a miss either since the local object data is still valid, and the Not-Modified reply is quite small.

One serious problem for cache hierarchies is mismatched freshness parameters. Consider a cache C using ``strict'' freshness parameters so its users get maximally current data. C has a sibling S with less strict freshness parameters. When an object is requested at C, C might find that S already has the object via an ICP query and ICP HIT response. C then retrieves the object from S.

In an HTTP/1.0 world, C (and C's client) will receive an object that was never subject to its local freshness rules. Neither HTTP/1.0 nor ICP provides any way to ask only for objects less than a certain age. If the retrieved object is stale by Cs rules, it will be removed from Cs cache, but it will subsequently be fetched from S so long as it remains fresh there. This configuration miscoupling problem is a significant deterrent to establishing both parent and sibling relationships.

HTTP/1.1 provides numerous request headers to specify freshness requirements, which actually introduces a different problem for cache hierarchies: ICP still does not include any age information, neither in query nor reply. So S may return an ICP HIT if its copy of the object is fresh by its configuration parameters, but the subsequent HTTP request may result in a cache miss due to any Cache-control: headers originated by C or by C's client. Situations now emerge where the ICP reply no longer matches the HTTP request result.

In the end, the fundamental problem is that the ICP query does not provide enough information to accurately predict whether the HTTP request will be a hit or miss. In fact, the current ICP Internet Draft is very vague on this subject. What does ICP HIT really mean? Does it mean ``I know a little about that URL and have some copy of the object?'' Or does it mean ``I have a valid copy of that object and you are allowed to get it from me?''

So, what can be done about this problem? We really need to change ICP so that freshness parameters are included. Until that happens, the members of a cache hierarchy have only two options to totally eliminate the ``access denied'' messages from sibling caches:

  1. Make sure all members have the same refresh_rules parameters.
  2. Do not use miss_access at all. Promise your sibling cache administrator that your cache is properly configured and that you will not abuse their generosity. The sibling cache administrator can check his log files to make sure you are keeping your word.
If neither of these is realistic, then the sibling relationship should not exist.

11.11 Cannot bind socket FD NN to *:8080 (125) Address already in use

This means that another processes is already listening on port 8080 (or whatever you're using). It could mean that you have a Squid process already running, or it could be from another program. To verify, use the netstat command:

        netstat -naf inet | grep LISTEN
That will show all sockets in the LISTEN state. You might also try
        netstat -naf inet | grep 8080
If you find that some process has bound to your port, but you're not sure which process it is, you might be able to use the excellent lsof program. It will show you which processes own every open file descriptor on your system.

11.12 icpDetectClientClose: ERROR xxx.xxx.xxx.xxx: (32) Broken pipe

This means that the client socket was closed by the client before Squid was finished sending data to it. Squid detects this by trying to read(2) some data from the socket. If the read(2) call fails, then Squid konws the socket has been closed. Normally the read(2) call returns ECONNRESET: Connection reset by peer and these are NOT logged. Any other error messages (such as EPIPE: Broken pipe are logged to cache.log. See the ``intro'' of section 2 of your Unix manual for a list of all error codes.

11.13 icpDetectClientClose: FD 135, 255 unexpected bytes

These are caused by misbehaving Web clients attempting to use persistent connections. Squid-1.1 does not support persistent connections.

11.14 How come Squid doesn't work with NTLM Authorization.

We are not sure. We were unable to find any detailed information on NTLM (thanks Microsoft!), but here is our best guess:

Squid transparently passes the NTLM request and response headers between clients and servers. The encrypted challenge and response strings most likely encode the IP address of the client. Because the proxy is passing these strings and is connected with a different IP address, the authentication scheme breaks down. This implies that if NTLM authentication works at all with proxy caches, the proxy would need to intercept the NTLM headers and process them itself.

If anyone knows more about NTLM and knows the above to be false, please let us know.

11.15 The default parent option isn't working!

This message was received at squid-bugs:

If you have only one parent, configured as:
        cache_host xxxx parent 3128 3130 no-query default
nothing is sent to the parent; neither UDP packets, nor TCP connections.

Simply adding default to a parent does not force all requests to be sent to that parent. The term default is perhaps a poor choice of words. A default parent is only used as a last resort. If the cache is able to make direct connections, direct will be preferred over default. If you want to force all requests to your parent cache(s), use the inside_firewall option:

        inside_firewall none

11.16 ``Hot Mail'' complains about: Intrusion Logged. Access denied.

``Hot Mail'' is proxy-unfriendly and requires all requests to come from the same IP address. You can fix this by adding to your squid.conf:

        hierarchy_stoplist hotmail.com

11.17 My Squid becomes very slow after it has been running for some time.

This is most likely because Squid is using more memory than it should be for your system. When the Squid process becomes large, it experiences a lot of paging. This will very rapidly degrade the performance of Squid. Memory usage is a complicated problem. There are a number of things to consider.

First, examine the Cache Manager Info ouput and look at these two lines:

        Number of TCP connections:      121104
        Page faults with physical i/o: 16720
Note, if your system does not have the getrusage() function, then you will not see the page faults line.

Divide the number of page faults by the number of connections. In this case 16720/121104 = 0.14. Ideally this ratio should be in the 0.0 - 0.1 range. It may be acceptable to be in the 0.1 - 0.2 range. Above that, however, and you will most likely find that Squid's performance is unacceptably slow.

If the ratio is too high, you will need to make some changes to lower the amount of memory Squid uses.

11.18 WARNING: Failed to start 'dnsserver'

This could be a permission problem. Does the Squid userid have permission to execute the dnsserver program?

You might also try testing dnsserver from the command line:

        > echo oceana.nlanr.net | ./dnsserver
Should produce something like:
        $name oceana.nlanr.net
        $h_name oceana.nlanr.net
        $h_len 4
        $ipcount 1
        132.249.40.200
        $aliascount 0
        $ttl 82067
        $end

11.19 Sending in Squid bug reports

Bug reports for Squid should be sent to the squid-bugs alias. Any bug report must include

crashes and core dumps

There are two conditions under which squid will exit abnormally and generate a coredump. First, a SIGSEGV or SIGBUS signal will cause Squid to exit and dump core. Second, many functions include consistency checks. If one of those checks fail, Squid calls abort() to generate a core dump.

Many people report that Squid doesn't leave a coredump anywhere. This is likely because of ``resource limits.'' These limits can usually be changed in shell scripts. The command to change the resource limits is usually either limit or limits. Sometimes it is a shell-builtin function, and sometimes it is a regular program. Also note that you can set resource limits in the /etc/login.conf file on FreeBSD and maybe other BSD systems.

To change the coredumpsize limit you might use a command like:

        limit coredumpsize unlimited
or
        limits coredump unlimited

The core dump file will be left in either one of two locations:

  1. The current directory when Squid was started
  2. The first cache_dir directory if you have used the cache_effective_user option.
If you cannot find a core file, then either Squid does not have permission to write in its current directory, or perhaps your shell limits (csh and clones) are preventing the core file from being written. If you suspect the current directory is not writable, you can add
        cd /tmp
to your script which starts Squid (e.g. RunCache).

Once you have located the core dump file, use a debugger such as dbx or gdb to generate a stack trace:


tirana-wessels squid/src 270% gdb squid /T2/Cache/core
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.15.1 (hppa1.0-hp-hpux10.10), Copyright 1995 Free Software Foundation, Inc...
Core was generated by `squid'.
Program terminated with signal 6, Aborted.

[...]

(gdb) where
#0  0xc01277a8 in _kill ()
#1  0xc00b2944 in _raise ()
#2  0xc007bb08 in abort ()
#3  0x53f5c in __eprintf (string=0x7b037048 "", expression=0x5f <Address 0x5f out of bounds>, line=8, filename=0x6b <Address 0x6b out of bounds>)
#4  0x29828 in fd_open (fd=10918, type=3221514150, desc=0x95e4 "HTTP Request") at fd.c:71
#5  0x24f40 in comm_accept (fd=2063838200, peer=0x7b0390b0, me=0x6b) at comm.c:574
#6  0x23874 in httpAccept (sock=33, notused=0xc00467a6) at client_side.c:1691
#7  0x25510 in comm_select_incoming () at comm.c:784
#8  0x25954 in comm_select (sec=29) at comm.c:1052
#9  0x3b04c in main (argc=1073745368, argv=0x40000dd8) at main.c:671

If possible, you might keep the coredump file around for a day or two. It is often helpful if we can ask you to send additional debugger output, such as the contents of some variables.

11.20 Debugging Squid

If you believe you have found a non-fatal bug (such as incorrect HTTP processing) please send us a section of your cache.log with debugging to demonstrate the problem. The cache.log file can become very large, so alternatively, you may want to copy it to an FTP or HTTP server where we can download it.

It is very simple to enable full debugging on a running squid process. Simply use the -k debug command line option:

        % ./squid -k debug
This causes every debug() statement in the source code to write a line in the cache.log file. You also use the same command to restore Squid to normal debugging.

To enable selective debugging (e.g. for one source file only), you need to edit squid.conf and add to the debug_options line. Every Squid source file is assigned a different debugging section. The debugging section assignments can be found by looking at the top of individual source files, or by reading the file doc/debug-levels.txt (correctly renamed to debug-sections.txt for Squid-2). You also specify the debugging level to control the amount of debugging. Higher levels result in more debugging messages. For example, to enable full debugging of Access Control functions, you would use

        debug_options ALL,1 28,9
Then you have to restart or reconfigure Squid.

Once you have the debugging captured to cache.log, take a look at it yourself and see if you can make sense of the behaviour which you see. If not, please feel free to send your debugging output to the squid-users or squid-bugs lists.

11.21 FATAL: ipcache_init: DNS name lookup tests failed

Squid normally tests your system's DNS configuration before it starts server requests. Squid tries to resolve some common DNS names, as defined in the dns_testnames configuration directive. If Squid cannot resolve these names, it could mean:

  1. your DNS nameserver is unreachable or not running.
  2. your /etc/resolv.conf file may contain incorrect information.
  3. your /etc/resolv.conf file may have incorrect permissions, and may be unreadable by Squid.

To disable this feature, use the -D command line option.

Note, Squid does NOT use the dnsservers to test the DNS. The test is performed internally, before the dnsservers start.

11.22 FATAL: Failed to make swap directory /var/spool/cache: (13) Permission denied

Starting with version 1.1.15, we have required that you first run

        squid -z
to create the swap directories on your filesystem. If you have set the cache_effective_user option, then the Squid process takes on the given userid before making the directories. If the cache_dir directory (e.g. /var/spool/cache) does not exist, and the Squid userid does not have permission to create it, then you will get the ``permission denied'' error. This can be simply fixed by manually creating the cache directory.
        # mkdir /var/spool/cache
        # chown <userid> <groupid> /var/spool/cache
        # squid -z

Alternatively, if the directory already exists, then your operating system may be returning ``Permission Denied'' instead of ``File Exists'' on the mkdir() system call. This patch by Miquel van Smoorenburg should fix it.

11.23 FATAL: Cannot open HTTP Port

Either (1) the Squid userid does not have permission to bind to the port, or (2) some other process has bound itself to the port. Remember that root privileges are required to open port numbers less than 1024. If you see this message when using a high port number, or even when starting Squid as root, then the port has already been opened by another process. Maybe you are running in the HTTP Accelerator mode and there is already a HTTP server running on port 80? If you're really stuck, install the way cool lsof utility to show you which process has your port in use.

11.24 FATAL: All redirectors have exited!

This is explained in the Redirector section.

11.25 You've run out of swap file numbers.

Squid keeps an in-memory bitmap of disk files that are available for use, or are being used. The size of this bitmap is determined at run name, based on two things: the size of your cache, and the average (mean) cache object size.

The size of your cache is specified in squid.conf, on the cache_dir lines. The mean object size can also be specified in squid.conf, with the 'store_avg_object_size' directive. By default, Squid uses 13 Kbytes as the average size.

When allocating the bitmaps, Squid allocates this many bits:

        2 * cache_size / store_avg_object_size

So, if you exactly specify the correct average object size, Squid should have 50% filemap bits free when the cache is full. You can see how many filemap bits are being used by looking at the 'storedir' cache manager page. It looks like this:

        Store Directory #0: /usr/local/squid/cache
        First level subdirectories: 4
        Second level subdirectories: 4
        Maximum Size: 1024000 KB
        Current Size: 924837 KB
        Percent Used: 90.32%
        Filemap bits in use: 77308 of 157538 (49%)
        Flags:

Now, if you see the ``You've run out of swap file numbers'' message, then it means one of two things:

  1. You've found a Squid bug.
  2. Your cache's average file size is much smaller than the 'store_avg_object_size' value.

To check the average file size of object currently in your cache, look at the cache manager 'info' page, and you will find a line like:

        Mean Object Size:       11.96 KB

To make the warning message go away, set 'store_avg_object_size' to that value (or lower) and then restart Squid.

11.26 When using a username and password, I can not access some files.

If I try by way of a test, to access

        
        ftp://username:password@ftpserver/somewhere/foo.tar.gz
I get
        somewhere/foo.tar.gz: Not a directory. 

Use this URL instead:

        
        ftp://username:password@ftpserver/%2fsomewhere/foo.tar.gz

11.27 pingerOpen: icmp_sock: (13) Permission denied

This means your pinger program does not have root priveleges. You should either do this:

        % su
        # make install-pinger
or
        # chown root /usr/local/squid/bin/pinger
        # chmod 4755 /usr/local/squid/bin/pinger

11.28 What is a forwarding loop?

A forwarding loop is when a request passes through one proxy more than once. You can get a forwarding loop if

Forwarding loops are detected by examining the Via request header. Each cache which "touches" a request must add its hostname to the Via header. If a cache notices its own hostname in this header for an incoming request, it knows there is a forwarding loop somewhere. NOTE: A pair of caches which have the same visible_hostname value will report forwarding loops.

When Squid detects a forwarding loop, it is logged to the cache.log file with the recieved Via header. From this header you can determine which cache (the last in the list) forwarded the request to you.

One way to reduce forwarding loops is to change a parent relationship to a sibling relationship.

Another way is to use cache_host_acl rules. For example:

        # Our parent caches
        cache_peer A.example.com parent 3128 3130
        cache_peer B.example.com parent 3128 3130
        cache_peer C.example.com parent 3128 3130

        # An ACL list
        acl PEERS src A.example.com
        acl PEERS src B.example.com
        acl PEERS src C.example.com

        # Prevent forwarding loops
        cache_host_acl A.example.com !PEERS
        cache_host_acl B.example.com !PEERS
        cache_host_acl C.example.com !PEERS
The above configuration instructs squid to NOT forward a request to parents A, B, or C when a request is received from any one of those caches.

11.29 accept failure: (71) Protocol error

This error message is seen mostly on Solaris systems. Mark Kennedy gives a great explanation:

Error 71 [EPROTO] is an obscure way of reporting that clients made it onto your server's TCP incoming connection queue but the client tore down the connection before the server could accept it. I.e. your server ignored its clients for too long. We've seen this happen when we ran out of file descriptors. I guess it could also happen if something made squid block for a long time.

11.30 storeSwapInFileOpened: ... Size mismatch

Got these messages in my cache log - I guess it means that the index contents do not match the contents on disk.

1998/09/23 09:31:30| storeSwapInFileOpened: /var/cache/00/00/00000015: Size mismatch: 776(fstat) != 3785(object)
1998/09/23 09:31:31| storeSwapInFileOpened: /var/cache/00/00/00000017: Size mismatch: 2571(fstat) != 4159(object)

What does Squid do in this case?

NOTE, these messages are specific to Squid-2. These happen when Squid reads an object from disk for a cache hit. After it opens the file, Squid checks to see if the size is what it expects it should be. If the size doesn't match, the error is printed. In this case, Squid does not send the wrong object to the client. It will re-fetch the object from the source.

11.31 Why do I get fwdDispatch: Cannot retrieve 'https://www.buy.com/corp/ordertracking.asp'

These messages are caused by buggy clients, mostly Netscape Navigator. What happens is, Netscape sends an HTTPS/SSL request over a persistent HTTP connection. Normally, when Squid gets an SSL request, it looks like this:

        CONNECT www.buy.com:443 HTTP/1.0
Then Squid opens a TCP connection to the destination host and port, and the real request is sent encrypted over this connection. Thats the whole point of SSL, that all of the information must be sent encrypted.

With this client bug, however, Squid receives a request like this:

        GET https://www.buy.com/corp/ordertracking.asp HTTP/1.0
        Accept: */*
        User-agent: Netscape ...
        ...
Now, all of the headers, and the message body have been sent, unencrypted to Squid. There is no way for Squid to somehow turn this into an SSL request. The only thing we can do is return the error message.

Note, this browser bug does represent a security risk because the browser is sending sensitive information unencrypted over the network.


Previous Next Table of Contents