Groesbeek, view of the 'National Liberation Museum 1944-1945' in Groesbeek. © Ton Kersten
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How to hunt the Haggis

2012-10-22 (128) by Ton Kersten, tagged as humor

Most people are familiar with my love of Scotland, single malt and (of course) haggis. But most people do not have a clue what haggis is and when you tell them, they walk out in disgust.

But a colleague of mine found out that haggis is just an animal that can be hunted in the Scottish Highlands.

This is how it's done:

.....asked me how the haggis were hunted so I explained that there were two types of haggis, who, because they lived on the steep slopes of the Scottish Highlands, developed legs of different lengths on their left and right sides depending upon which way they travelled round the mountain to graze. With the knowledge of which type of haggis one was hunting, the procedure was quite simple.

A large 'catch fence' was erected around the base of the mountain and a piper was sent up the mountain to play his bagpipes while walking contrary to the normal direction of rotation of the haggis. This put the fear of G*d in to the wee creatures who tried to run away, but of course their short legs were now down-hill so they soon overbalanced and rolled down the mountain into the catch fence at the base where they were then easily caught and euthanized.

Thanks to Hendrik Jan Thomassen.

Resize a partition

2012-10-19 (127) by Ton Kersten, tagged as sysadm

I often have to increase the size of a virtual disk on a virtual machine. But I always seem to forget how to do it. I guess I have done it over a 100 times and I cannot remember exactly how I did it. So this blog entry is to help people on how to do this and as a reminder to myself.

This example is done on a virtual machine with CentOS 6, but it can be done on every Linux. And in the fdisk examples I have left out some of the not to interesting lines.

Oke, here we go:

First, shut down your virtual machine and increase the disk size. Then start your virtual machine and go to the console. Now you have a virtual machine with a new disk size, but the current partition table needs to be adjusted to the new disk size. I know it’s possible with parted, but I always seem to end up on systems where it’s not available. So I just use fdisk.

# fdisk /dev/sda

Now give the p command, which prints the partition table and make a note of the start cylinder of the Linux LVM partition. This is the partition we are going to increase.

Please be very careful This trick only works if the partition you want to resize is at the end of the disk and contains a logical volume type system.

Command (m for help): p

Disk /dev/sda: 17.2 GB, 17179869184 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          64      512000   83  Linux
/dev/sda2              65        2089    16264192   8e  Linux LVM

Delete the LVM partition (we will recreate this later)

Command (m for help): d
Partition number (1-5): 2

and create a new partition with the original starting point. The starting point should be the same, because all the partitions meta data is at the start of the partition.

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2

And fill in the start cylinder of the LVM partition we deleted above

First cylinder (1-25600, default 1): 65
Last cylinder, +cylinders or +size{K,M,G} (65-25600, default 25600):
Using default value 25600

and change the type to Linux LVM

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 8e
Changed system type of partition 2 to 8e (Linux LVM)

Command (m for help): p

Disk /dev/sda: 26.8 GB, 26843545600 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           2          64      262144   83  Linux
/dev/sda2              65        2089    24567892   8e  Linux LVM

If you agree with the new layout, write it to disk with the w command and quit with q. If it’s not the disk disk with the root volume on it, it could be possible that you can skip the next reboot. Just a partprobe could do the trick.

# reboot

First it’s needed to resize physical volume.

# pvresize /dev/sda2

Make sure you know how much free space you now have

# vgdisplay

Make a note of the “LV Name” of the logical volume you want to resize

# lvdisplay

Resize the logical volume. I use gigabytes as an example here.

# lvresize -L +[Size]GB [LV Name]

Resize the file system on the logical volume.

# resize2fs [LV Name]

MySQL backup error

2012-08-09 (126) by Ton Kersten, tagged as linux, mysql

After upgrading my MySQL database server from version 5.0.95 to 5.1.61 I suddenly got these errors in the backup logging.

mysqldump: Couldn't execute 'SELECT /*!40001 SQL_NO_CACHE */ * FROM `EVENTS`': Cannot
proceed because system tables used by Event Scheduler were found damaged at server start
(1577)
dbdump gave errorcode 2 for database 'information_schema'
2012-08-09 09:07:53 -> Finished MySQL backup on host 'xxx.tonkersten.com'

Hmm, no idea what has happened. I hope I didn't do something stupid.

Asking Google I found out that the information_schema tables where changed during the upgrade and that I could recreate the error with:

mysql> use information_schema
Database changed

mysql> SELECT /*!40001 SQL_NO_CACHE */ * FROM EVENTS;
ERROR 1577 (HY000): Cannot proceed because system tables used by Event Scheduler were found damaged at server start
mysql> Bye

So I tried to repair the error with:

mysql_upgrade -u root -h localhost -p --verbose

but still the same error.

Turns out that the MySQL server needs to be restarted for this to work.

Now I get

mysql> use information_schema
Database changed

mysql> SELECT /*!40001 SQL_NO_CACHE */ * FROM EVENTS;
Empty set (0.00 sec)
mysql> Bye

CDE is Open Source

2012-08-06 (125) by Ton Kersten, tagged as code, linux, news

Today the classic, and old, Common Desktop Environment (a.k.a. CDE) was released into the Open Source world.

You can get the very alpha version at SourceForge.

I haven't been able to get a running version by now, but I keep trying.

Good job, guys.

git status in the prompt

2012-07-23 (124) by Ton Kersten, tagged as code, git, linux, sysadm

Working with git a lot I decided I needed some git status in my prompt.

I searched the web and some solutions where almost what I wanted and this one by Sebastian Celis came very close.

But it didn't work with my version of zsh, because that didn't seem to understand the =~ operator.

I also think Sebastian makes things over complicated and so I changed some things aroud.

This is what I came up with:

First make sure this code is included in your ~/.zshenv file

prompt_git_info()
{
    unset __GIT_BRANCH
    unset __GIT_BRANCH_STATUS
    unset __GIT_BRANCH_DIRTY

    local st="$(git status 2>/dev/null)"
    if [[ -n "$st" ]]; then
        local -a arr
        arr=(${(f)st})

        if [[ $arr[1] = *Not\ currently\ on\ any\ branch.* ]]
        then
            __GIT_BRANCH='no-branch'
        else
            __GIT_BRANCH="${arr[1][(w)4]}"
        fi

        if [[ $arr[2] = *Your\ branch\ is* ]]
        then
            if [[ $arr[2] = *ahead* ]]
            then
                __GIT_BRANCH_STATUS='ahead'
            elif [[ $arr[2] = *diverged* ]]
            then
                __GIT_BRANCH_STATUS='diverged'
            else
                __GIT_BRANCH_STATUS='behind'
            fi
        fi

        if [[ $st = *nothing\ to\ commit* ]]
        then
            __GIT_BRANCH_DIRTY='0'
        else
            __GIT_BRANCH_DIRTY='1'
        fi
    fi

    if [[ -n "$__GIT_BRANCH" ]]
    then
        local s="("
        s+="$__GIT_BRANCH"
        case "$__GIT_BRANCH_STATUS"
        in
            ahead)      s+="↑"  ;;
            diverged)   s+="↕"  ;;
            behind)     s+="↓"  ;;
        esac
        if [[ "$__GIT_BRANCH_DIRTY" = "1" ]]
        then
            s+="⚡"
        fi
        s+=")"

        printf " %s%s" "%{${fg[yellow]}%}" $s
    fi
}

and set your prompt to something like this

PS1=$'$C_CYAN%n@%m$(prompt_git_info) $C_WHITE%2~$ $C_OFF'

When I now switch to a directory that is under control of git I get gt status messages in my prompt, like

tonk@mach (master) ~/dir$ git commit -a
[master fca5ac3] Nice, new stuff.
 6 files changed, 88 insertions(+), 12 deletions(-)
tonk@mach (master) ~/.dir$ git status
# On branch master
# Your branch is ahead of 'origin/master' by 1 commit.
#
nothing to commit (working directory clean)
tonk@mach (master) ~/.dir$

No network on CentOS 6

2012-07-17 (123) by Ton Kersten, tagged as linux, sysadm

When installing a minimal CentOS 6 system, minimal really, really means minimal. After a reboot the network interfaces do not start, so network connectivity is non existing.

Looking into that I noticed that the file /etc/sysconfig/network-scripts/ifcfg-eth0 contained

DEVICE=eth0
HWADDR=11:22:33:44:55:66
NM_CONTROLLED=yes
ONBOOT=no
BOOTPROTO=dhcp
TYPE=Ethernet
USERCTL=no
PEERDNS=yes
IPV6INIT=no

The lines that mess things up are NM_CONTROLLED=yes meaning the interfaces are managed with NetworkManager, which isn’t actually installed as part of a minimal install. You want a minimal install, you get a minimal install. And ONBOOT=no, meaning "do not start the interface on boot". How stupid is that!

The trick is to run something like system-config-network-tui to set the IP addresses manually, but as you might imagine, that's not installed either.

So you best edit /etc/sysconfig/network-scripts/ifcfg-eth0 by hand and set it to:

DEVICE=eth0
HWADDR=11:22:33:44:55:66
NM_CONTROLLED=no
ONBOOT=yes
BOOTPROTO=none
TYPE=Ethernet
USERCTL=no
PEERDNS=yes
IPV6INIT=no
IPADDR=192.168.0.1
NETMASK=255.255.255.0
GATEWAY=192.168.0.254
DNS1=192.168.0.254

The USERCTL=... line is optional: If set to yes it lets non-root users control the interface.

After setting this a service network restart will do the trick.

New version of We-Blog

2012-07-10 (122) by Ton Kersten, tagged as blog, code

Today I released version 0.8 of We-Blog.

I created a Google project and a Google discussion group.

Version 0.8 is now the stable branch and 0.9 the development branch.

What's new?

Well, to be really honest, not that much. I fixed some minor bugs and did a lot of code cleanup. Although the original code of Jaromir was very nice, there was some room for improvement. I removed a lot of double functions and variables and put them all together in a We.pm Perl module. Saves a lot of work with an update.

Finding key codes on Linux

2012-07-04 (121) by Ton Kersten, tagged as code, linux, sysadm

It often happens that I get into a situation where I need to know key codes of pressed keys. On my Mac that's simple. Just use the Key Codes by Many Tricks.

But on Linux I constantly was trying to find out which key produced what.

So I ended up writing a program for that. I started of in the shell, but that ended up being rather tricky and unnecessary complicated. So I redid the whole thing in C.

This is the result

/*
 * Program     : code.c
 * Author      : Ton Kersten
 */

#include <stdio.h>
#include <curses.h>

#define DONE    'q'
#define ESC     0x1b
#define SPC     0x20

char ch;

main()
{
    printf("Press '%c' to quit!\n\n", DONE);

    /*
     * Put the terminal in raw mode, with no echo
     */
    system("stty raw -echo");

    /*
     * Print the header
     */
    printf("%4s\t%4s\t%4s\t%4s\r\n", "Char", " Hex", " Oct", " Dec");
    printf("%4s\t%4s\t%4s\t%4s\r\n", "----", "----", "----", "----");

    /*
     * Set the initial loop value to something odd
     */
    ch = DONE-1;
    while ( ch != DONE )
    {   ch = getchar();

        /*
         * Character read. Display it. Look out for < 0x20
         */
        if ( ch < SPC )
        {   if ( ch == ESC )
            {   /*
                 * Esc. Just say 'Esc'
                 */
                printf("%-4s\t0x%02x\t%04o\t%04d\r\n",
                        "Esc", ch, ch, ch);
            }
            else
            {   /*
                 * < ' '. Print Control character
                 */
                printf("^%-c\t0x%02x\t%04o\t%04d\r\n",
                        ch-1+'A', ch, ch, ch);
            }
        }
        else
        {   /*
             * Normal character. Display it normally
             */
            printf("%-4c\t0x%02x\t%04o\t%04d\r\n",
                        ch, ch, ch, ch);
        }
    }

    /*
     * Put the terminal back to something usefull
     */
    system("stty sane echo");
}

And this is an example of the output

Press 'q' to quit!

Char     Hex     Oct     Dec
----    ----    ----    ----
Esc     0x1b    0033    0027
O       0x4f    0117    0079
P       0x50    0120    0080
Esc     0x1b    0033    0027
[       0x5b    0133    0091
2       0x32    0062    0050
4       0x34    0064    0052
~       0x7e    0176    0126
q       0x71    0161    0113

Shell tip

2012-07-04 (120) by Ton Kersten, tagged as code, linux, sysadm

During one of my teaching sessions a student asked me if it was possible to find the number of spaces in a variable.

As with all questions in Linux and UNIX the answer is a simple

Of course that's possible. In UNIX and Linux everything is possible.

With some sed or awk this can be done within seconds. But I wanted it done completely within the shell, in this case bash.

This is what I came up with

P="John and Paul and Ringo and George where the Beatles"
R=${P//[! ]/}       # Remove everything that is NOT a space
echo ${#R}          # Show the number of characters (spaces) that are left

And this also works in the Korn shell (ksh) and the Z-shell (zsh).

Burning VIDEO_TS on OSX

2012-07-01 (119) by Ton Kersten, tagged as mac os x

I was trying to burn a folder with a VIDEO_TS directory onto a DVD. But in a way that it will start in a normal DVD player as well as starting automagically. And this all had to be done on Apple's OSX.

I googled a little and tried some things and this is what I can up with:

hdiutil makehybrid -udf         \
    -udf-volume-name DVD_NAME   \
    -o MY_DVD.iso               \
    /path/to/VIDEO_TS/parent/folder

Make sure that /path/to/VIDEO_TS/parent/folder is the path to the folder containing the VIDEO_TS folder, not the VIDEO_TS folder itself.`

After that, the resulting MY_DVD.iso can easily be burned with burn