Petr’s blog about Linux

Sometimes I’m using the serial connection to my server if anything goes wrong. It’s because I don’t have a monitor/TV attached to it.

I have little problems to set it up using Debian in GRUB2 after I upgraded to grub-pc

So here is a short way how to do it:

Edit file containing configuration in Debian: /etc/default/grub

Don’t forget to run update-grub after change.

This page contains few information how to create crypted disk using dm_crypt, lvm, gpg with remote key stored on http server.
The advantage is to have key, used for unlocking crypted disk(s), somewhere on the server instead have it on USB.

* You can easily delete this key if your disks are stolen and nobody can access them any longer…
* If you use USB stick to save key then you need to have it connected to the machine with the cyphered disks every reboot – usually it will be plugged all the time to the server which destroy all security.
* Keys are downloaded automatically every reboot from remote HTTP server (if not your disks will remain locked)

All commands were tested on Debian and should be also applicable on other distributions.

Read more…

Look at small how-to install cobbler with yum on RHEL 4.6 from scratch.

Install the most RHEL 4.6 or CentOS 4.6 with default partitioning and custom installation (unselect all possible packages during installation procedure). Diable firewall and SELinux.

• Enable DVD repository by changing the line in /etc/yum.repos.d/CentOS-Media.repo
enabled=1
• Install yum
mount /media/cdrom
• Download packages and install them:
mkdir /var/tmp/cobbler-4.6
cd /var/tmp/cobbler-4.6
rpm -i
./python-elementtree-1.2.6-5.el4.centos.x86_64.rpm \
./python-urlgrabber-2.9.8-2.noarch.rpm ./sqlite-3.3.6-2.x86_64.rpm \
./python-sqlite-1.1.7-1.2.1.x86_64.rpm \
./yum-metadata-parser-1.0-8.el4.centos.x86_64.rpm \
./centos-yumconf-4-4.5.noarch.rpm \
./yum-2.4.3-4.el4.centos.noarch.rpm \
./createrepo-0.4.4-2.noarch.rpm
yum clean all
mkdir /var/tmp/rhel4_repo/
ln -s /media/cdrom/RedHat/RPMS/ /var/tmp/rhel4_repo/RPMS
createrepo /var/tmp/rhel4_repo/
cat >/etc/yum.repos.d/RHEL-4.6-Media.repo <<+
[rhel4-media]
name=RHEL4 - Media
baseurl=file:///var/tmp/rhel4_repo/
gpgcheck=0
enabled=1
+

createrepo /var/tmp/cobbler-4.6/
cat >>/etc/yum.repos.d/my.repo <<+
[my-repo]
name=My Repository
baseurl=file:///var/tmp/cobbler-4.6/
gpgcheck=0
enabled=1
+
• Install necessary software from DVD

[/cc]

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.orig

yum -y install wget mc
yum -y install httpd tftp-server mod_python python-devel createrepo rsync mkisofs
yum -y install perl-Digest-SHA1 perl-Digest-HMAC perl-Socket6 perl-Time-HiRes sysstat perl-libwww-perl
yum -y install libart_lgpl freetype libpng
yum -y install logrotate perl-DateManip
yum -y install cman
yum -y install dhcp bind
yum -y install memtest86+

yum -y install cobbler
yum -y install munin munin-node php-ldap
chkconfig munin-node on
yum -y install yum-utils
yum -y install syslinux
• Disable firewall (just for sure):
chkconfig --level 2345 iptables off
service iptables stop
• Change line in /etc/cobbler/settings to match the IP of the server:
default_password_crypted: "$1$pH3........0B2HB/"
default_name_servers: [192.168.0.129]
manage_dhcp: 1
manage_dns: 1
manage_forward_zones: [my.domain.cz]
manage_reverse_zones: [192.168.0]
next_server: 192.168.0.129
pxe_just_once: 1
server: 192.168.0.129
register_new_installs: 0
xmlrpc_rw_enable: 1
• Start cobbler and apache daemon:
/etc/init.d/cobblerd start
/etc/init.d/httpd start
chkconfig httpd on
• Change ‘disable’ to ‘no’ in /etc/xinetd.d/tftp
disable                 = yes

Cobbler/DHCPd/bind configuration

• Change listening interface for dhcpd in /etc/sysconfig/dhcpd:
DHCPDARGS=eth0;
• Modify file /etc/cobbler/dhcp.template according your needs:
subnet 192.168.0.0 netmask 255.255.255.0 {
     option routers             10.226.23.1;
     option domain-name         "my.domain.cz";
     option domain-name-servers 192.168.0.129;
     option subnet-mask         255.255.255.0;
     range dynamic-bootp        192.168.0.200 192.168.0.254;
     filename                   "/pxelinux.0";
     default-lease-time         21600;
     max-lease-time             43200;
     next-server                $next_server;
}
• Modify /etc/cobbler/named.template like:
options {
...
#          listen-on port 53 { 127.0.0.1; };
...
#          allow-query     { localhost; };
           forwarders { 10.226.32.44; };
...
};
cobbler sync
service xinetd restart
chkconfig dhcpd on
chkconfig named on

Now you should run

cobbler check

and see something like that:

[root@c2virtud tmp]# cobbler check
No setup problems found
Manual review and editing of /var/lib/cobbler/settings is recommended to tailor cobbler to your particular configuration.

Cobbler repository+ installation

cobbler import --name=RHEL4.6-x86_64-AS --mirror=/media/cdrom/
cobbler repo add --mirror=/var/tmp/cobbler-4.6/ --name=my-repo
cobbler reposync
cobbler image add --name=Memtest86+-1.26 --file=/tftpboot/memtest86+-1.26 --image-type=direct
cobbler profile copy --name=RHEL4.6-AS-x86_64 --newname=NGP_RHEL4.6-AS-x86_64
cobbler profile copy --name=rescue-RHEL4.6-AS-x86_64 --newname=NGP_rescue-RHEL4.6-AS-x86_64
cobbler profile edit --name=NGP_RHEL4.6-AS-x86_64 --repos="my-repo"
cobbler profile edit --name=NGP_rescue-RHEL4.6-AS-x86_64 --repos="my-repo"
cobbler sync
• Edit /etc/yum.repos.d/RHEL-4.6-Media.repo and change one line like:
baseurl=file:///var/www/cobbler/ks_mirror/RHEL4.6-x86_64-AS/RedHat
• Then run:
yum clean all

PXE configuration

• Make this the first line of /etc/cobbler/pxe/pxedefault.template,pxeprofile.template,pxesystem.template to enable serial connection:
SERIAL 0 115200

Cobbler WebUI

• Set root password for web access:
htdigest /etc/cobbler/users.digest "Cobbler" root
• Change line in /etc/cobbler/modules.conf:
module = authn_configfile
service cobblerd restart
service httpd restart

Cobbler host specification

cobbler system add --comment="c3virt01ce01 machine" --name=c3virt01ce01 --hostname=c3virt01ce01 --netboot-enabled=1 --profile=NGP_RHEL4.6-AS-x86_64 --name-servers=192.168.0.129 --static=0 --kickstart=/var/lib/cobbler/kickstarts/legacy.ks
cobbler system edit --name c3virt01ce01 --interface=eth0 --mac=00:0c:29:68:78:96 --ip=192.168.0.10 --netmask=255.255.255.0  --static=1 --dns-name=c3virt01ce01.my.domain.cz
cobbler system edit --name c3virt01ce01 --interface=eth1 --mac=00:0c:29:68:78:b4 --ip=192.168.1.10 --netmask=255.255.255.0 --static=1
cobbler system edit --name c3virt01ce01 --interface=eth2 --mac=00:0c:29:68:78:aa --ip=192.168.2.10 --netmask=255.255.255.0 --static=1
cobbler system edit --name c3virt01ce01 --interface=eth3 --mac=00:0c:29:68:78:be --static=0
cobbler sync

Hope it will be possible to use PXE boot to install machines.

It’s happened to me one time, that I want to trim margins from PDF document.

It was a manual for Panasonic G1 camera: http://ftp.xvx.cz/pub/docs/my/panasonic_g1.pdf

You can see huge margins there, because it was officially written for A5 paper and they create manual for A4.

See the picture:

I used pdfcrop script from Heiko Oberdiek, which can easily trim margins.

Here is the result:

I hope this can be useful for somebody who needs this…
KDE pdf viewer Okular, has the function “Trim Margins”, which works very well, but you can not save the PDF…

My photo collection is stored on the server and accessed by cifs protocol to my notebooks. I’m using digiKam to browse my collection in KDE.

This software is storing all thumbnails in ~/.thumbnails/ according http://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html and create sqlite database where it stores all information about photos.

• The advantage is, that these thumbnails can be also used by other KDE viewers (like Gwenview).
• The disadvantage can be that other viewers can generate new thumbnails which are no longer useful an the size of that directory can grow…

I decided to write script which can delete all useless thumbnails and keep only the ones used by digiKam. The reason is simple – I don’t want remove all thumbnails and regenerate them again only from digiKam, because I have more than 35k photos so it take a long time…

Here is my digiKam collection configuration:

This script deletes all thumbnails of the photos in

which are not on network shares :

(It preserves all the thumbnails of photos stored on network share, which take ages to create because of network or which are not changing, and delete all locally ones)

thumbnails_delete.pl

Maybe you can find it helpful…