Category Archives: Tips and tricks

Splitting and catting a tar file into 2 Gb chunks

Post migrated from my old site:

If you for some weird reason (which I have) would like to back large files up to a FAT32 volume and need maximum 2 Gb files, or for some other reason would like to chop up your backup file into chunks, use the following command:

tar -cvaf - *|split -b 2000m - volume.tar

To unpack use:

cat volume.tar* | tar xv

And wait a long time…

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Shell scripting 101 for Linux

Post migrated from my old site:

Call me a stupid, but I always forget in what order to put the # and ! on the first line of a shell script.

So, to prevent this in the future, I will remember it here. The first line should be:

#!/bin/bash

Adding a disk to your logical volumes

Post migrated from my old site:

I found this information quite useful:
http://www.linuxnetadmin.com/2008/01/how-to-add-disk-space-with-lvm-on-linux.html
https://ext4.wiki.kernel.org/index.php/Frequently_Asked_Questions

Firefox fix for Fedora 12

Post migrated from my old site:

If your Firefox automatically starts offline after updating NetworkManager, you can solve this by entering

about:config

in the Firefox url bar and modify

toolkit.networkmanager.disable

to true.

Fedora – Installing VirtualBox with Yum

Post migrated from my old site:

Instructions to install VirtualBox (http://www.virtualbox.org) with Yum on Fedora can be found here:
http://www.virtualbox.org/wiki/Linux_Downloads

Debian 5 – Using the internal editor of Midnight Commander (mc)

Post migrated from my old site:

By default in Debian 5 mc is configuration to use nano which somehow I cannot get used to.
To fix this, go into the menu by pressing F9, Options > Configuration, Use internal edit.

Adding a Samba user

Post migrated from my old site:

Samba can be used to share folders with Windows systems.

To add a user to Samba, use

smbpasswd -a <username>

Setting up an encrypted RAID 5 on Ubuntu 10.10

Post migrated from my old site:

Recently I started on configuring an encrypted RAID 5 on Ubuntu 10.10 Server. These were the steps I took:

First, install the required packages:

sudo apt-get install mdadm gddrescue cryptsetup lvm2

I used fdisk to partition each disk as a “Linux raid autodetect” partition.

sudo fdisk /dev/sdb

for each device (in my case /dev/sdb /dev/sdc /dev/sdd and /dev/sde). First use option “n” to add a partition, option “t”to change it to type “fd” and “w” to write the changes to disk.

Next step is to create the RAID5 device:

sudo mdadm /dev/md0 --create -n 4 -l 5 -z 244198584 -c 256 /dev/sd{b..e}1

244198584 is the number of kilobyte of a single disk obtained with:

sudo hdparm -I /dev/sdb

Once it has been created, check its status by

sudo cat /proc/mdstat

and

sudo mdadm --detail /dev/md0

Wait until the status reports that the RAID has been fully build.

Next step is to create a physical volume by:

sudo pvcreate /dev/md0

To create a volume group, use:

sudo vgcreate rawlargevg /dev/md0

To create a logical volume, use:

sudo lvcreate -n rawsharelv -L 732585984k rawlargevg

Obtain the size by using:

sudo vgs --units k

To randomize the disk content use:

sudo ddrescue /dev/urandom /dev/rawlargevg/rawsharelv urandomminglog

This might take a long time, after it is done, start setting up the encrypted volume:

sudo cryptsetup -c aes-cbc-essiv:sha256 -y -s 256 luksFormat /dev/rawlargevg/rawsharelv

Next step is to open it:

sudo cryptsetup luksOpen /dev/rawlargevg/rawsharelv encsharedev

And format it:

sudo mkfs.ext4 -m 0 /dev/mapper/encsharedev

After it is done formatting, create a mounting directory:

sudo mkdir /srv/raid

Now edit the /etc/crypttab file to include:

encsharedev /dev/rawlargevg/rawsharelv none luks

And edit /etc/fstab to include:

/dev/mapper/encsharedev /srv/raid ext4 rw 0 0

Reboot and done you are with setting up your encrypted RAID.

References to pages I used:

Postfix on KPN Direct ADSL

Hi,

I had a lot of trouble setting up Postfix so that it would relay my mail (sending only). I am using KPN Direct ADSL and have documented some tricks here for Ubuntu 12.10.

KPN’s support answer is somewhat useful but not that much:
http://kpn-customer.custhelp.com/app/answers/detail/a_id/13372

The three different addresses they are mentioning for the relayhost, confused me a lot. The right relayhost to use is: mail.kpnmail.nl.

My /etc/postfix/main.cf looks like this:

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
append_dot_mydomain = no
readme_directory = no
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
myhostname = <hostname>
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = <externaldomain>, <hostname>, localhost
relayhost = [mail.kpnmail.nl]
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
default_transport = relay
relay_transport = relay
inet_protocols = all
sender_canonical_maps=hash:/etc/postfix/sender_canonical

Please make sure that you replace <hostname> and <externaldomain> with your machine’s hostname and external domain URL.

The last I found with http://www.whatismyip.com/ to get my external ip address and to get your external domain URL:

host <ip-address>

Notice that I had to change the default_transport and relay_transport to error to:

default_transport = relay
relay_transport = relay

The other thing I had to do is to set the following to change rewrite the from field as KPN does not accept the <user>@<hostname> that your Ubuntu machine provides:

sender_canonical_maps=hash:/etc/postfix/sender_canonical

To set up your sender_canonical file, follow these instructions:
http://ubuntuforums.org/archive/index.php/t-38429.html

Useful background information can be found here:
http://www.postfix.org/

Mac OS X Mountain Lion Subversion missing

If you are like me missing Subversion in Mountain Lion, find the solution here:
http://superuser.com/questions/455214/where-is-svn-on-os-x-mountain-lion

As I have Xcode installed, I took the option to install the command line tools and it works.

Regards,
Jeroen