Groesbeek, view of the 'National Liberation Museum 1944-1945' in Groesbeek. © Ton Kersten
Fork me on GitHub
Posts tagged as sysadm

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

    unset __GIT_BRANCH
    unset __GIT_BRANCH_DIRTY

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

        if [[ $arr[1] = *Not\ currently\ on\ any\ branch.* ]]

        if [[ $arr[2] = *Your\ branch\ is* ]]
            if [[ $arr[2] = *ahead* ]]
            elif [[ $arr[2] = *diverged* ]]

        if [[ $st = *nothing\ to\ commit* ]]

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

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

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


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:


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.

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;

    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'
                        "Esc", ch, ch, ch);
            {   /*
                 * < ' '. Print Control character
                        ch-1+'A', ch, ch, ch);
        {   /*
             * Normal character. Display it normally
                        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).

sed tips and tricks

2012-06-22 (116) by Ton Kersten, tagged as code, linux, sysadm

I'm creating a Puppet Starter Kit with some standard manifests included and a complete set of documentation. All documentation should be written in Markdown and will be served by Markdoc. But I want to generate all Markdown files from the Puppet manifests, so I only need to document the manifest file. Generating the Markdown is not that difficult, except that I kept ending up with empty lines at the top of the manifest code and I wanted to get rid of those. Of course this should be done with sed, because the whole generation process is written in bash. When playing around with sed I found

sed '/./,$!d' filename

which, I think, is genius in it's simplicity. After you find something, do not remove. Life in UNIX and Linux is nice!

Read more »

Puppet updates

2012-06-18 (115) by Ton Kersten, tagged as code, puppet, sysadm

When working with Puppet and a VCS (like git and SVN) it's nice to have a simple way of updating the Puppet tree.

My tree is always in /etc/puppet and owned by user and group puppet. User puppet is allowed to checkout the complete tree from git or subversion.

I have created two one-liners to update the complete tree and make sure all rights are still correct.


# update_svn
su - puppet -c 'cd /etc/puppet; svn up; cd doc; ../bin/gendoc'


# update_git
su - puppet -c 'cd /etc/puppet; git pull; cd doc; ../bin/gendoc'

But, of course, it's not handy to type update_git today and update_svn tomorrow. And I also don't want a path to /etc/puppet/bin.

The solution is a very simple one, as always:

cd /usr/local/bin
ln -s /etc/puppet/bin/update_git pupdate

and now I only have to type pupdate and things work out.

Fix a lot of rights

2012-06-18 (114) by Ton Kersten, tagged as linux, sysadm

A customer called and wanted help with an error they made.

The error was simple, they typed:

chmod -R 660 /

and now things broke. Of course things broke. If they would not brake that would be very weird.

Luckily they had a second server and a simple one-liner stole all the rights from this second server and and we could put these on the broken one.

The oneliner

find / -depth -printf 'chmod %m\t\t-- "%p"\nchown %u:%g\t-- "%p"\n' >

produces output like this

chmod 644       -- "/etc/sysconfig/kdump"
chown root:root -- "/etc/sysconfig/kdump"
chmod 644       -- "/etc/sysconfig/rhn/sources"
chown root:root -- "/etc/sysconfig/rhn/sources"
chmod 644       -- "/etc/sysconfig/rhn/sources.rpmforge.txt"
chown root:root -- "/etc/sysconfig/rhn/sources.rpmforge.txt"

Running this script on the broken server left us with something that was working.


dpkg -x <package name>

on all cached packages in /var/cache and after that a

dpkg --reconfigure -a

Solved the rest.

Pheeeuuwww, we were lucky smiley

Updated Pygments

2012-05-16 (112) by Ton Kersten, tagged as blog, puppet, pygments, sysadm

I'm using Pygments for quite some time now and I just noticed there was a new version available (1.5). I installed that and I was wondering if there would be a lexer included for Puppet. Well, it wasn't, but a short Google action directed me to the Pygments lexer for the Puppet DSL.

Of course my old CentOS 5 system with Python 2.6 doesn't want to install this, so I hacked the Puppet lexer into Pygments.

Here's an example of the result:

class generic::ssh {
    $ssh_service       = hiera("ssh_service")
    $ssh_packages      = hiera("ssh_packages")
    $ssh_debug         = hiera("ssh_debug",         "undef")
    $permit_root_login = hiera("permit_root_login", "no")
    $ssh_users         = hiera_array("ssh_users",   "undef")
    $ssh_groups        = hiera_array("ssh_groups",  "undef")

    package { $ssh_packages:
        ensure => present,
        before => File["/etc/ssh/sshd_config"],

    file { "/etc/ssh/sshd_config":
        ensure  => present,
        content => template("generic/sshd_config.erb"),
        notify  => Service["${ssh_service}"],

    service { $ssh_service:
        ensure     => running,
        enable     => true,
        hasrestart => true,
        hasstatus  => true,

and an example of the Hiera Yaml file:


# SSH Settings
permit_root_login    : 'no'
ssh_service          :
                       - 'sshd'
ssh_users            :
                       - 'root'
                       - 'tonk'
ssh_groups           :
                       - 'wheel'
ssh_packages         :
                       - 'openssh'
                       - 'openssh-clients'
                       - 'openssh-server'

Nice smiley

Switching to tmux

2011-07-24 (104) by Ton Kersten, tagged as sysadm

Some time ago I was fighting my .screenrc again. I wanted to change the status line, but it was hardly possible to read and understand what I typed hardly half a year ago. The screen config file is not exactly poetry.

While searching the web to find how to change the status line I ran into tmux and I thought: "Let's give it a try". And after the very simple compile I started configuring it. What a surprise I was in for. This config file could be read, understood and changed. Man, this is good.

One of the first things I changed was the default Prefix key Ctrl-B. I changed it to Alt-A, so I can still use all the control keys with Vim and in the terminal.

Read more »

FreeBSD PXE boot Part 2

2011-06-09 (96) by Ton Kersten, tagged as freebsd, puppet, pxe, sysadm

Some posts ago I wrote that I was busy to find out how a FreeBSD machine can be PXE-ed from a Linux server. Well, I found that some time ago, but I didn't have the time to type it here, yet. Well, as always, once you know how it's done, it's quite simple. But because a lot of the FreeBSD documentation is very old (talking about FreeBSD 4, 5 and 6) it takes some time to find it all.

Read more »