Apache 1.3.41 HostnameLookups bug?

This weekend a scheduled maintenance in the data centre took out the name servers. I wasn't worried because all the names we needed to resolve in order to keep serving pages were in /etc/hosts.

Sure enough, during the maintenance alarms started going off. Web pages, static or dynamic, were taking in excess of 5 seconds to be served. We checked /etc/nsswitch.conf to make sure forward lookups were being resolved by /etc/hosts instead of DNS:

hosts: files dns

We then inspected the access log and we could see that some entries had host names instead of IP addresses. This was odd since reverse DNS lookups were turned off in Apache:

HostnameLookups Off

A colleague suggested it could be our LogFormat configuration:

LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined

The documentation is pretty clear that %h will only do a reverse lookup if HostnameLookups is turned on:

If HostnameLookups is set to On, then the server will try to determine the hostname and log it in place of the IP address.

Nevertheless, we replaced %h with %a. That didn't solve the issue - requests still took little more than 5 seconds to be fulfilled. The millisecond part of the response time looked right to me, so I went on to read the resolv.conf man page and found this bit very interesting:

timeout:n
sets the amount of time the resolver will wait for a response from a remote name server before retrying the query via a different name server. Measured in seconds, the default is RES_TIMEOUT (currently 5, see <resolv.h>).

Now I was pretty much convinced that Apache was playing tricks on us. I double-checked all our Allow statements to make sure we weren't using hostnames, since the manual says it will do a reverse lookup in this case:

This configuration will cause the server to perform a double reverse DNS lookup on the client IP address, regardless of the setting of the HostnameLookups directive.

We only had Allow statements for the usual restricted URLs (server-status etc) and even then, were only using IP addresses.

I decided to disable the lookups in source code, since this was starting to look like a bug. In src/main/http_core.c, line 728, I commented the reverse lookup call and replaced it with a fake response:

// hptr = gethostbyaddr((char *)iaddr, sizeof(struct in_addr), AF_INET);
hptr = NULL;

I did the same on line 825:
// hptr = gethostbyaddr((char *)iaddr, sizeof(struct in_addr), AF_INET);
hptr = NULL;

The web server went back to serving static and dynamic objects in the normal time, tens of milliseconds. I deployed the newly compiled Apache to all servers and went back to my weekend.

This hack obviously breaks all functionality that depends on reverse IP address lookups so, if I have some time, I will analyse this condition and, if it is a bug, submit a patch to the chaps at the Apache Foundation.

QEMU/KVM mouse not working?

This guy knows the answer:

$ export SDL_VIDEO_X11_DGAMOUSE=0

For me, because I use a physical device for a disk and didn't want to give myself permission on the device:

$ sudo SDL_VIDEO_X11_DGAMOUSE=0 qemu-launcher

My mouse stopped working after I configured Xinerama and display rotation on X (I had alsoi upgraded to Ubuntu 9.04 but I didn't test my VM before fiddling with xorg.conf).

XOrg configuration for Samsung LA32A450C1

This guy nailed it. I had only just found the manual page for my Samsung 32" LCD TV and was still googling for a tool to find the modeline.

I've only added the option to turn off nvidia's logo to his X configuration. Too good:

Section "Monitor"
Identifier "SamsungTV"
ModelName "Samsung LCD TV"
ModeLine "1360x768@60" 85.8 1360 1440 1552 1792 768 771 777 795 +hsync +vsync
Option "dpms"
EndSection

Section "Device"
Identifier "NVIDIAVideocard0"
Driver "nvidia"
Option "ModeValidation" "DFP-0: NoDFPNativeResolutionCheck"
Option "ExactModeTimingsDVI" "TRUE"
#### 100 DPI
Option "UseEDIDDpi" "FALSE"
Option "DPI" "100 x 100"
Option "NoLogo" "True"
EndSection

Section "Screen"
Identifier "Screen0"
Device "NVIDIAVideocard0"
Monitor "SamsungTV"
DefaultDepth 24
SubSection "Display"
Depth 24
##### Native Res Samsung 1360x768@60
Modes "1360x768@60" "1280x720" "1024x768" "800x600" "640x480"
EndSubSection
EndSection

RHN's yum update fails

I've noticed that quite often Red Hat's yum will fail for no good reason. For example it will just show an error like:

# yum update
(...)

Error Downloading Packages:
samba-common - 3.0.28-1.el5_2.1.x86_64: failed to retrieve getPackage/samba-common-3.0.28-1.el5_2.1.x86_64.rpm from rhel-x86_64-server-5
error was [Errno 14] HTTP Error 404: Not Found

When that's the case, retrying a few times usually does the trick.

I have actually opened a ticket with RHN's support and they've told me these are "temporary errors". Temporary or not they are pretty annoying so here's what I do.

1. Retry manually until you're happy with the list of packages that will be updated
2. Run yum in a while loop so that it retries until it succeeds:

# while ! (yum update -y) ; do echo TRY AGAIN; done

Be aware that if that too many retries can cause your RHN subscription to be temporarily locked-out. I find the benefit too great to care.

Mytharchive: cannot burn a dvd

I've been playing with MythTV again. Configuring it still is a major pain in the arse - there seems to be something wrong with the channel scanner that throws you off the track. I think.

Anyway, after recording a few programs I wanted to burn a DVD. My first attempt failed because Mytharchive tries writing to /dev/dvd by default. I solved this problem by linking /dev/dvd to my DVD device.

Tried again and Mytharchive refused to enter the burn DVD menu, showing the error below:

Mytharchive: cannot burn a dvd, the last run failed to create a dvd

WTF? A bit harsh on the error flagging, I'd say. So after searching around I found some people with the same problem but none of the helpful people would tell how to clear the error. Here's what you do.

1. Quit mythfrontend
2. Open a command prompt and:

mysql -u root
use mythconverg;
update settings set data='' where value='MythArchiveLastRunStatus';
update settings set data='' where value='MythArchiveLastRunType';

3. Go back to mytharchive and try again. This time it will let you proceed to the DVD burn menus.

How to avoid overlapping rsync instances

Running rsync as a cron job is probably as popular as sliced bread. For small intervals, however, you risk having a second instance start before the first one has finished, beginning a downward spiral of bandwidth and processes.

To avoid multiple instances getting in each other's way there's a simple solution using flock. Example without lock (may cause overlapping instances):

*/5 * * * * /usr/bin/rsync --delete -a source_server:/source/path/ /dst/path/

Example using flock:

*/5 * * * * flock -xn /tmp/example.lock -c '/usr/bin/rsync --delete -a source_server:/source/path/ /dst/path/'

In the second example, if a rsync instance runs for more than 5 minutes, flock will fail and thus not execute a second rsync process.

This can be used for pretty much any shell problem where locking helps. Have a read on the flock man page for other examples.

No time? No worries!

IIS asp.net v2.0 fake 403 and 404 errors

After installing an ASP.NET v2.0 application I tried to browse to it but IIS wouldn't show the page and spit this 403 error instead:

The website declined to show this webpage

Now, there are a few causes to this problem. The most common is when the user forgets to add an index page to the site or, to add the index page to the list of "Enable default content page" under IIS.

Mr. Ian Tinsley found a more sinister cause that has the following symptom: if you browse to an existing .aspx file, ISS will return a 404 error code, even though the file exists. A good way to check if this is your case is to place a static file (htm or gif etc) in your site and try browsing it; if it shows you the static file then you probably have a fake 403/404 scenario.

To make sure, go to Web Service Extensions under IIS and check if ASP.NET v2.x is listed:




The tricky bit is: even if ASP.NET v2.x is not listed above, the v2.x extension still shows on the application properties. So if you don't have it above, you need to run aspnet_regiis.exe:



Running with -ir will help keep your asp.net v1.1 stuff running and still install v2:

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis.exe -ir

Sun x4450

With a range of options for the Intel Tigerton Quad-core Xeon processors, the Sun x4450 fitted the recommendations for our new postgres database servers. Solaris 10 was chosen by default as the operating system - why complicate the setup by mixing vendors, right?

Well, long story made short: I've ditched Solaris 10 x86_64 in favour of Red Hat Enterprise 5.1. Why? For one thing the Solaris 10 installation was frustratingly complicated.

Performing an installation via serial console requires you to redirect output from the BNC to the System in the BIOS settings. Then the manual states you should choose grub menu's option "ttb". Of course the manual meant "ttyb". But it is actually a typo AND an error: you must choose ttya or all you'll see after boot is "Sun Solaris 5.10" and nothing else.



Once the serial console installation is finished and the system reboots you have another obstacle. The boot process stops at this error message:

Bad PBR sig

Reboot and Select proper Boot device or
Insert Boot Media in selected Boot device and press a key

Googling around (Sun's KB was useless) I found someone with the same problem reporting that a GUI installation didn't show that error. Very well, I configured the firewall to allow Sun's network KVM:

8890 TCP Remote Console
9000 TCP Remote Console
9001 TCP Remote Console
9002 TCP Remote Console
9003 TCP Remote Console
69 UDP TFTP (for firmware upgrades)
161 UDP SNMP (for monitoring)

As the anonymous poster reported, this did solve the problem. Now to install postgres for x86_64. Hmm. Doesn't run - complains about missing libraries. Probably just need to run crle to set-up the location of the 64bit libraries. Where are they, where are they... WTF? There are no x86_64 libraries installed in my Solaris 10 for x86_64. I check around with `file' and yeah: all bloody system libraries are 32 bits.

I confess I didn't try too hard after this. A day later and we had postgres running on RHEL 5.1. And yes, with a 64bit binary and libraries.

To Sun's credit, the hardware looks a beauty, even though you have to assemble the whole thing by yourself: memory cards, SAS card, Fibre Channel card, hard disks and whatever extras you bought. What a pain in the arse. Compared to the other Dell servers with pre-installed RHEL 5.1 we recently bought the Sun experience is pathetic: the Dells where up on the same day versus 1 week for Sun.

Nagios checks for LSI RAID with MegaCli

I am pretty sure there is a SNMP object in Dell's DRAC 5/PERC to inform about the status of your RAID volumes and physical disks. I'm not too fond of using SNMP with Nagios so I wrote a check script that uses the MegaCli linux i386 binary (from the LSI web site) to report the status of the RAID on our Dell/Red Hat Linux servers.

Here's what you need:

• perl interpreter in /usr/bin/perl
• nagios' utils.pm in /usr/local/nagios/libexec/
• perl module Time::HiRes (cpan; install Time::HiRes)
• sudo in /usr/bin/
• MegaCli in /opt/MegaRAID/MegaCli/MegaCli64

You'll also need the check_dellperc in /usr/local/nagios/libexec. Change the paths as you see fit.

#!/usr/bin/perl -wT
#
# CHECK DELL/MegaRAID DISK ARRAYS ON LINUX
# $Id: check_dellperc 142 2008-03-17 22:25:46Z thiago $
#

BEGIN {
 $ENV{'PATH'} = '/usr/bin';
 $ENV{'ENV'} = '';
 $ENV{'BASH_ENV'} = '';
 $ENV{'IFS'} = ' ' if ( defined($ENV{'IFS'}) ) ;
}

use strict;
use lib "/usr/local/nagios/libexec";
use utils qw($TIMEOUT %ERRORS &print_revision &support &usage);

use Getopt::Long;

use Time::HiRes qw ( tv_interval gettimeofday );

use vars qw($opt_h $help $opt_V $version);
use vars qw($PROGNAME $SUDO $MEGACLI);

$PROGNAME = "check_dellperc";
$SUDO = "/usr/bin/sudo";
$MEGACLI = "/opt/MegaRAID/MegaCli/MegaCli64";

my $t_start = [gettimeofday];

Getopt::Long::Configure('bundling');
GetOptions
 ("V"   => \$opt_V,  "version"    => \$opt_V,
  "h"   => \$opt_h,  "help"       => \$opt_h,
 );


if ( $opt_V ) {    print_revision($PROGNAME, '$Id: check_dellperc 142 2008-03-17 22:25:46Z thiago $');
 exit $ERRORS{'OK'};

} elsif ( $opt_h ) {
 print_help();
 exit $ERRORS{'OK'};
}

my $TIMEOUT = $utils::TIMEOUT;
my $start_time = time();
# TODO: add timeout option#if ( $opt_t && $opt_t =~ /^([0-9]+)$/ ) {
#    $TIMEOUT = $1;
#}


# Check state of Logical Devices
my $status = "PERC OK";
my $perfdata = "";
my $errors = $ERRORS{'OK'};
my $vd = "";
my $vds = "";

open(MROUT, "$SUDO $MEGACLI -LDInfo -Lall -aALL -NoLog|");
if (!<MROUT>) {
 print("Can't run $MEGACLI\n");
 exit $ERRORS{'UNKNOWN'};
}

while (<MROUT>) {
 my $line = $_;
 chomp($line);

 if ($line =~ /^Virtual Disk: (\d+)/) {
     $vd = $1;
     next;
 }

 if ($vd =~ /^[0-9]+$/) {
     if ($line =~ /^State: (\w+)/) {
         $vds = $1;            #TODO: verbose print("State for VD #$vd is $vds\n");
         $perfdata = $perfdata." VD$vd=$vds";
         if ($vds !~ /^Optimal$/) {
             $errors = $ERRORS{'CRITICAL'};
             $status = "RAID ERROR";
             #TODO: verbose print("Error found: $status. Skipping remaining Virtual Drive tests.\n");
             last;
         } else {
             $vd = ""; $vds = "";
         }
     }
 }
}
close(MROUT);

# Check state of Physical Drives
my $count_type;my $pd = "";
my $pds = "";

open(MROUT, "$SUDO $MEGACLI -PDList -aALL -NoLog|");
if (!<MROUT>) {
 print("Can't run $MEGACLI\n");
 exit $ERRORS{'UNKNOWN'};
}

while (<MROUT>) {
 my $line = $_;
 chomp($line);

 if ($line =~ /^Device Id: (\d+)/) {
     $pd = $1;
     next;
 }

 if ($pd =~ /^[0-9]+$/) {
     if ($line =~ /^(Media Error|Other Error|Predictive Failure) Count: (\w+)/) {
         $count_type = $1;
         $pds = $2;            #TODO: verbose print("$count_type count for device id #$pd is $pds\n");
         $perfdata = $perfdata." PD$pd=$count_type;$pds";
         if ($pds != 0) {
             if ($errors == $ERRORS{'OK'}) {
                 $status = "DISK ERROR";
                 $errors = $ERRORS{'WARNING'};
             }
         }
     }
 }
}
close(MROUT);

# Got here OK
#
my $t_end = [gettimeofday];
print "$status| time=" . (tv_interval $t_start, $t_end) . "$perfdata\n";
exit $errors;


sub print_usage
{
 print "Usage: $PROGNAME\n";
}


sub print_help
{
 print_revision($PROGNAME, '$Revision: 142 $ ');
 print "Copyright (C) 2007 Westfield Ltd\n\n";
 print "Check Dell/MegaRaid Disk Array plugin for Nagios\n\n";

 print_usage();
 print <<USAGE
-V, --version
    Print program version information
-h, --help
    This help screen


Example:
    $PROGNAME

USAGE
;

}

After installing the script above and changing the paths to match your system, edit your sudoers file (sudo /usr/sbin/visudo) and comment the following line:

# Defaults requiretty

If you are doing NRPE checks, the line above will prevent the script from running sudo because there is no TTY associated with it. There is probably a way around it that doesn't involve disabling this security feature - if you find out please tell me.

While in the sudoers file, also add the following two lines:

nagios ALL=(ALL) NOPASSWD: /opt/MegaRAID/MegaCli/MegaCli64 -PDList -aALL -NoLog
nagios ALL=(ALL) NOPASSWD: /opt/MegaRAID/MegaCli/MegaCli64 -LDInfo -Lall -aALL –NoLog

If you run NRPE with a user different than "nagios", change the lines above to match it.

That is it, basically. Before adding it to your NRPE checks, give it a try:

$ sudo -u nagios /usr/local/nagios/libexec/check_dellperc
PERC OK| time=0.189185 VD0=Optimal VD1=Optimal PD0=Media Error;0 PD0=Other Error;0 PD0=Predictive Failure;0 PD1=Media Error;0 PD1=Other Error;0 PD1=Predictive Failure;0 PD2=Media Error;0 PD2=Other Error;0 PD2=Predictive Failure;0 PD3=Media Error;0 PD3=Other Error;0 PD3=Predictive Failure;0 PD4=Media Error;0 PD4=Other Error;0 PD4=Predictive Failure;0 PD5=Media Error;0 PD5=Other Error;0 PD5=Predictive Failure;0

It should return a status of zero (unless, of course, your RAID is b0rken):
$ echo $?
0

It is not a toy

From the book "Things that work but you wouldn't have bet on before actually trying".


$ mplayer your_movie.iso

Teamsite 6.7.1 SP1 won't start

After installing Teamsite 6.7.1 SP1 on a Solaris 10 machine I tried starting the service to check out the new version. Sadly, the service wouldn't start, dumping a core and printing this message:

[crit] file vhost.c, line 190, assertion "rv == APR_SUCCESS" failed Abort - core dumped /app/teamsite/iw-home/iw-webd/bin/iw.webd start: iwwebd could not be started

In my case, adding "dns" to the "hosts:" line on /etc/nsswitch.conf solved the problem:

hosts: files dns

A little bee tells me that you can also edit /iw-webd/conf/iwwebd.conf.template and change "_default_" on the VirtualHost entry to "*":

<VirtualHost _default_:__IWWEBD_HTTPS_PORT__>

to

<VirtualHost *:__IWWEBD_HTTPS_PORT__>

I didn't try it but that's also the recommendation from an Interwoven's KB article (support account needed).

TCP wrappers: refused connect from ...

I've used inetd + tcp wrappers + netcat a number of times for migration of TCP-based services to a new server. It goes something like this:

1. Get the service running on the new box
2. Point the DNS entry (or IP address of the server on clients) to the new server
3. Stop the service on the old box
4. Enable the redirection using inetd
   

For number 4 and HTTP redirection, an entry like the one below in your /etc/inetd.conf is usually enough:

http stream tcp nowait nobody /usr/bin/tcpd /usr/bin/netcat new-server 80

You then leave the old server running until no more clients connect to it. I do that by inspecting the syslog entries and looking for the netcat redirections. Last time, however, I was seeing these:

Jan 30 14:20:04 old-box netcat[16769]: [ID 947420 mail.warning] refused connect from 189.201.77.65

And sure enough, I started to get complaints that some clients were no longer able to connect to the service. I had left /etc/hosts.allow empty on purpose since there was no need to restrict the service to specific hosts.

After some digging through the tcp wrappers readme, I suspected that the version of tcpd on this SunOS 5.8 (Solaris 8) had been compiled with -DPARANOID. If defined, PARANOID will cause tcpd to reject hosts whose IP address don't resolve to a name (using reverse DNS).

I downloaded the tcp_wrappers source, recompiled without -DPARANOID and installed the newly compiled binary. The refused connection entries were gone from the log and the clients confirmed they were able to reach the server once again.

MSMQ error:0xc00e0027

After installing windows 2003 Service Pack 2 on a production box I started getting errors 0xc00e0027 when the application tried to access the queues. A number of related articles gave different solutions but what worked for me was reinstalling Message Queuing from the Control Panel.

I had to re-create my queues too, since they were wiped-out when I removed the component.

VMWare Workstation on Debian AMD64

I've just upgraded to the x86_64 Debian architecture (AMD64). When installing vmware workstation for x86_64 it complained about some missing libraries but the installation finished nevertheless.

However the application would not open any VMs, spitting this error:

/usr/lib/vmware/bin/vmware-vmx: error while loading shared libraries: libX11.so.6: cannot open shared object file: No such file or directory

Turns out some of the VMWare binaries need 32bit libraries, even on the 64bit version. This post on vmware's knowledge base gave a solution for Red Hat distros. On Debian the solution is analogous: you just need to install the package ia32-libs.

You will need to re-install VMWare so that it regenerates the vmmon kernel module. The vmware-any-any patch is not needed.

Broadcom 4311 on Linux

The Dell Inspiron 1501 I bought after seeing the ad on TV nearly a year ago is a good bang for your buck, except when it comes to the wireless card shipped with this notebook.

Because of the efforts of the ndiswrapper and bcm43xx developers I managed to use the wi-fi card until I started using the AMD64 binaries for Debian Etch.

If you are buying a notebook and plan to use Linux in it, stay away from the Broadcom wireless cards or any other cards that require loading a firmware at run-time.

I got tired of struggling and I'm now waiting for my Intel 2915ABG mini-pci card to arrive in the mail. Hardware is too cheap nowadays to justify wasting my time getting a vendor to work.

Checking your round-robin DNS with nagios

Nagios comes with a plugin, check_dns, that allows you to perform DNS-based checks. It is really useful to check that your DNS server is responding and, with option switch "-a", that it is providing the expected IP address to specified queries.

$ ./check_dns -H example.com.au -a 1.2.3.4
DNS OK: 0.157 seconds response time. example.com.au returns 1.2.3.4|time=0.157327s;;;0.000000

If your host name has more than one IP address associated with it - no problem -, just add it to the command line. For example:

./check_dns -H example.com.au -a 1.2.3.4,9.8.7.6
DNS OK: 0.157 seconds response time. example.com.au returns 1.2.3.4,9.8.7.6|time=0.157327s;;;0.000000

However, if your host name is using a round-robin DNS configuration you can't predict the response reliably. Try google.com.au, for instance.

$ dig google.com.au
;; ANSWER SECTION:
google.com.au.          230     IN      A       72.14.235.104
google.com.au.          230     IN      A       72.14.207.104
google.com.au.          230     IN      A       72.14.203.104

Then check_dns will only work 1/3 of the time:

./check_dns -H google.com.au -a 72.14.235.104,72.14.207.104,72.14.203.104
DNS OK: 0.035 seconds response time. google.com.au returns 72.14.235.104,72.14.207.104,72.14.203.104|time=0.035388s;;;0.000000

The other 2/3 you will see:

$ ./check_dns -H google.com.au -a 72.14.235.104,72.14.207.104,72.14.203.104
DNS CRITICAL - expected '72.14.235.104,72.14.207.104,72.14.203.104' but got '72.14.203.104,72.14.235.104,72.14.207.104'

I thought that really sucked because it stopped me from using this very nice feature of check_dns. So I patched check_dns.c in Nagios Plugins 1.4.10 to include the command line option "-o". When you specify this option, check_dns will sort the DNS response so you can still use -a.

$ ./check_dns -H google.com.au -o -a 72.14.203.104,72.14.207.104,72.14.235.104
DNS OK: 0.112 seconds response time. google.com.au returns 72.14.203.104,72.14.207.104,72.14.235.104|time=0.111538s;;;0.000000

I've sent the patch to the Nagios developers list - hopefully it will get incorporated into future releases. If not, you can download the patch here and the patched source here.

Think your secure email provider keeps your secrets?

Think again.

"Bad user" on Solaris 10 crontab

An account used for an application could not run its cron jobs. In /var/cron/log all I could see was:

! bad user (wondapp) Tue Nov 13 03:23:00 2007

I checked /etc/cron.allow (which didn't exist) and the user's shell in /etc/passwd but the problem turned out to be in /etc/shadow. The user was listed as:

wondapp:*LK*:::::::

This was because a password was never set for it. I just edited it to read:

wondapp:NP:::::::

Which still doesn't make a valid password but doesn't lock-out the account either. Cron jobs for wondapp work now.

Nagios check_http SSL check

Nagios plugin check_http has a -C option that allows you to be warned when the SSL certificate is about to expire. It always annoyed me, however, that the expiry date was printed in crazy-ass US date format (which doesn't make any sense).

I've altered the source code so that it prints the expiry date in human readable format.

The changes were made to file plugins_sslutils.c. You can download a patch for version 1.4.10 here. Or just download the changed file; it might work for other versions too.