When writing this, it occurred to me how unnecessary this all is. I will explain below. First, I will describe the old way.

Here is the c source code, as written for our backup script, bsbackup.sh:

// Wrapper for the bsbackup.sh shell script, to be able to run it as root when
// started from a webserver, for example. Set the resulting executable to SUID
// root.
 
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <error.h>
 
int main(int argc, char *argv[], char *envp[])
{
    int set_uid_result;
    int effective_user_id;
    int execute_script_error;
    char* script;
 
    effective_user_id = geteuid();
 
    // Set real and effective user ID
    set_uid_result = setreuid(effective_user_id, effective_user_id);
 
    if (set_uid_result != 0)
    {
        printf("Failed to set user id\n");
        return 1;
    }
 
    script = "/usr/local/sbin/bsbackup.sh";
 
    // This does not return on success.
    execve(script, argv, envp);
    execute_script_error = errno;
 
    // Show a fancy error message.
    error(execute_script_error, execute_script_error, script);
 
    // Shouldn't be necceary, but you never know.
    return 1;
}

To compile:

gcc -o bsbackup bsbackup.c

You can then run this inside PHP:

// The 2>&1 makes all error messages appear on stdout, for easy capturing.
passthru('/usr/local/sbin/bsbackup usb_backup 2>&1');

As I said, when writing this, it all became very clear to me that it is quite useless. One can also install sudo, run visudo and put this in (assuming your webserver runs as www-data, like on (Debian and Ubuntu):

www-data ALL = NOPASSWD: /usr/local/sbin/bsbackup.sh

Then in PHP, just run this:

passthru('sudo /usr/local/sbin/bsbackup.sh usb_backup 2>&1');

I haven’t tested whether specifying the parameters after the script in the passthru actually works, but I think so. If not, you can just write a wrapper script around the command you’re going to execute.

See what you like best

Error: Could not stat() command file ‘/var/lib/nagios3/rw/nagios.cmd’!

Do:

/etc/init.d/nagios3 stop
dpkg-statoverride --update --add nagios www-data 2710 /var/lib/nagios3/rw
dpkg-statoverride --update --add nagios nagios 751 /var/lib/nagios3
/etc/init.d/nagios3 start

source.

To fix it, you can install exim4, but configure this line in /etc/default/exim4:

QUEUERUNNER='queueonly'

aptitude search '~i!~E' | grep -v "i A" | cut -d " " -f 4

First install Xen:

aptitude -P install xen-hypervisor-4.0-amd64 linux-image-xen-amd64 xen-tools

Debian Sqeeuze uses Grub 2, and the defaults are wrong for Xen. The Xen hypervisor (and not just a Xen-ready kernel!) should be the first entry, so do this:

mv -i /etc/grub.d/10_linux /etc/grub.d/50_linux

Then, disable the OS prober, so that you don’t get entries for each virtual machine you install on a LVM.

echo "" >> /etc/default/grub
echo "# Disable OS prober to prevent virtual machines on logical volumes from appearing in the boot menu." >> /etc/default/grub
echo "GRUB_DISABLE_OS_PROBER=true" >> /etc/default/grub
update-grub2

Per default (on Debian anyway), Xen tries to save-state the VM’s upon shutdown. I’ve had some problems with that, so I set these params in /etc/default/xendomains to make sure they get shut down normally:

XENDOMAINS_RESTORE=false
XENDOMAINS_SAVE=""

In /etc/xen/xend-config.sxp I enabled the network bridge (change an existing or commented-out line for this). I also set some other useful params (for me):

(network-script network-bridge)
(dom0-min-mem 196)
(dom0-cpus 1)
(vnc-listen '127.0.0.1')
(vncpasswd '')

Then I edited /etc/xen-tools/xen-tools.conf. This config contains default values the xen-create-image script will use. Most important are:

# Virtual machine disks are created as logical volumes in volume group universe (LVM storage is much faster than file)
lvm = universe
 
install-method = debootstrap
 
size   = 50Gb      # Disk image size.
memory = 512Mb    # Memory size
swap   = 2Gb    # Swap size
fs     = ext3     # use the EXT3 filesystem for the disk image.
dist   = `xt-guess-suite-and-mirror --suite` # Default distribution to install.
 
gateway    = x.x.x.x
netmask    = 255.255.255.0
 
# When creating an image, interactively setup root password
passwd = 1
 
# I think this option was this per default, but it doesn't hurt to mention.
mirror = `xt-guess-suite-and-mirror --mirror`
 
mirror_maverick = http://nl.archive.ubuntu.com/ubuntu/
 
# Ext3 had some weird settings per default, like noatime. I don't want that, so I changed it to 'defaults'.
ext3_options     = defaults
ext2_options     = defaults
xfs_options      = defaults
reiserfs_options = defaults
btrfs_options    = defaults
 
# let xen-create-image use pygrub, so that the grub from the VM is used, which means you no longer need to store kernels outside the VM's. Keeps this very flexible.
pygrub=1
 
# scsi is specified because when creating maverick for instance, the xvda disk that is used can't be accessed. 
# The scsi flag causes names like sda to be used.
scsi=1

I created the following script to easily let me make VM’s:

#!/bin/bash
 
# Script to easily create VM's. Hardy, maverick and Lenny are tested
 
dist=$1
hostname=$2
ip=$3
 
if [ -z "$hostname" -o -z "$ip" -o -z "$dist" ]; then
  echo "No dist, hostname or ip specified"
  echo ""
  echo "Usage: $0 dist hostname ip"
  exit 1
fi
 
if [ "$dist" == "hardy" ]; then
  serial_device="--serial_device xvc0"
fi
 
xen-create-image $serial_device --hostname $hostname --ip $ip --vcpus 2 --pygrub --dist $dist

At this point, you can reboot (well, you could earlier, but well…).

Usage of the script should be simple. When creating a VM named ‘machinex’, start it and attach console:

xm create -c /etc/xen/machinex.cfg

You can escape the console with ctrl-]. Place a symlink in /etc/xen/auto to start the VM on boot.

As a sidenote: when creating a lenny, the script installs a xen kernel in the VM. When installing maverick, it installs a normal kernel. Normals kernels since version 2.6.32 (I believe) support pv_ops, meaning they can run on hypervisors like Xen’s.

First see this for some general explantion.

I used this config file:

# /etc/exim4/update-exim4.conf.conf
#
# Edit this file and /etc/mailname by hand and execute update-exim4.conf
# yourself or use 'dpkg-reconfigure exim4-config'
#
# Please note that this is _not_ a dpkg-conffile and that automatic changes
# to this file might happen. The code handling this will honor your local
# changes, so this is usually fine, but will break local schemes that mess
# around with multiple versions of the file.
#
# update-exim4.conf uses this file to determine variable values to generate
# exim configuration macros for the configuration file.
#
# Most settings found in here do have corresponding questions in the
# Debconf configuration, but not all of them.
#
# This is a Debian specific file
 
dc_eximconfig_configtype='internet'
dc_other_hostnames='existingdomain.com'
dc_local_interfaces='127.0.0.1'
dc_readhost=''
dc_relay_domains=''
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost=''
CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname=''
dc_mailname_in_oh='true'
dc_localdelivery='mail_spool'

Also remember to put that existingdomain.com in /etc/mailname.

The scrAPI script calls a simple PHP script to add the extracted comment to the WordPress DB. The next step was copying the script to the development server (which has command-line PHP and the MySQL daemon running). Of course, the development server (which runs Debian Lenny) didn’t have the scrapi package installed. So, I thought I’d install the rubygems package and be done after gem install scrapi.

It seemed to install just fine, but… it just won’t fucking work! Adding require 'rubygems' to the script doesn’t work either.

This whole thing reminded of a similar occasion a while back when RubyGems kept fucking up everything until we discovered through Google that the version of RubyGems shipped with Debian simply couldn’t handle the whole dependency graph we had to deal with (or something). We had to grab a newer version from Debian backports to make the whole thing work. Another couple of hours wasted on a botched up package management system.

This time I’ve already wasted enough time. I’m ready to change my PHP guestbook comment import code to some XML-RPC hack instead so that I can run it on my laptop.