nimmis/centos repository overview

⁠CentOS with some extra commands

This is a docker image of CentOS with a working init process and syslog

⁠Why use this image

The unix process ID 1 is the process to receive the SIGTERM signal when you execute a

docker stop <container ID>

if the container has the command CMD ["bash"] then bash process will get the SIGTERM signal and terminate. All other processes running on the system will just stop without the possibility to shutdown correclty

⁠my_init init script

In this container i have a scipt that handles the init process an uses the supervisor system⁠ to start the daemons to run and also catch signals (SIGTERM) to shutdown all processes started by supervisord. This is a modified version of an init script made by Phusion. I've modified it to use supervisor in stead of runit. There are also two directories to run scripts before any daemon is started.

⁠Run script once /etc/my_runonce

All executable in this directory is run at start, after completion the script is removed from the directory

⁠Run script every start /etc/my_runalways

All executable in this directory is run at every start of the container, ie, at docker run and docker start

⁠Permanent output to docker log when starting container

Each time the container is started the content of the file /tmp/startup.log is displayed so if your startup scripts generate vital information to be shown please add that information to that file. This information can be retrieved anytime by executing docker logs <container id>

⁠cron daemon

In many cases there are som need of things happening att given intervalls, default no cron processs is started in the standard centos image. In this image cron is running together with logrotate to stop the logdfiles to be to big on log running containers.

⁠syslog-ng

No all services works without a syslog daemon, if you don't have one running those messages is lost in space, all messages sent via the syslog daemon is saved in /var/log/syslog

⁠Docker fixes

Also there are fixed (besideds the init process) assosiated with running centos inside a docker container.

⁠New commands autostarted by supervisord

To add other processes to run automaticly, add a file ending with .conf in /etc/supervisor/conf.d/ with a layout like this (/etc/supervisor/conf.d/myprogram.conf)

[program:myprogram]
command=/usr/bin/myprogram

myprogram is the name of this process when working with supervisctl.

Output logs std and error is found in /var/log/supervisor/ and the files begins with the <-stdout|-stderr>superervisor*.log

For more settings please consult the manual FOR supervisor⁠

⁠starting commands from /etc/init.d/ or commands that detach with my_service

The supervisor process assumes that a command that ends has stopped so if the command detach it will try to restart it. To work around this problem I have written an extra command to be used for these commands. First you have to make a normal start/stop command and place it in the /etc/init.d that starts the program with

/etc/init.d/command start or
service command start

and stops with

    /etc/init.d/command stop or
    service command stop

Configure the configure-file (/etc/supervisor/conf.d/myprogram.conf)

[program:myprogram]
command=/my_service myprogram

There is an optional parameter, to run a script after a service has start, e.g to run the script /usr/local/bin/postproc.sh av myprogram is started

    [program:myprogram]
    command=/my_service myprogram /usr/local/bin/postproc.sh

⁠Output information to docker logs

The console output is owned by the my_init process so any output from commands woun't show in the docker log. To send a text from any command, either at startup och during run, append the output to the file /var/log/startup.log, e.g sending specific text to log

echo "Application is finished" >> /var/log/startup.log

or output from script

/usr/local/bin/myscript >> /var/log/startlog.log


> docker run -d --name centos nimmis/centos
> docker logs centos
*** open logfile
*** Run files in /etc/my_runonce/
*** Run files in /etc/my_runalways/
*** Running /etc/rc.local...
*** Booting supervisor daemon...
*** Supervisor started as PID 9
2015-08-04 11:34:06,763 CRIT Set uid to user 0
*** Started processes via Supervisor......
crond                            RUNNING    pid 13, uptime 0:00:04
syslog-ng                        RUNNING    pid 12, uptime 0:00:04

> docker exec centos sh -c 'echo "Testmessage to log" >> /var/log/startup.log'
> docker logs centos
    *** open logfile
    *** Run files in /etc/my_runonce/
    *** Run files in /etc/my_runalways/
    *** Running /etc/rc.local...
    *** Booting supervisor daemon...
    *** Supervisor started as PID 9
    2015-08-04 11:34:06,763 CRIT Set uid to user 0
    *** Started processes via Supervisor......
    crond                            RUNNING    pid 13, uptime 0:00:04
    syslog-ng                        RUNNING    pid 12, uptime 0:00:04

*** Log: Testmessage to log
    >

⁠Added som normaly used commands

There are a number of commands that most uses and adds to their build, in this build I've added som commonly used packages

Extra included packages are

• wget
• curl
• zip/unzip
• git
• vim
• nano
• psmisc
• less
• patch
• software-properties-common

⁠Installation

This continer should normaly run as a daemon i.e with the -d flag attached

docker run -d nimmis/centos

but if you want to check if all services has been started correctly you can start with the following command

docker run -ti nimmis/centos

the output, if working correctly should be

docker run -ti nimmis/centos
*** open logfile
*** Run files in /etc/my_runonce/
*** Run files in /etc/my_runalways/
*** Running /etc/rc.local...
*** Booting supervisor daemon...
*** Supervisor started as PID 11
2015-01-02 10:45:43,750 CRIT Set uid to user 0
*** Started processes via Supervisor......
crond                            RUNNING    pid 15, uptime 0:00:02
syslog-ng                        RUNNING    pid 14, uptime 0:00:02

pressing a CTRL-C in that window or running docker stop <container ID> will generate the following output

*** Shutting down supervisor daemon (PID 11)...
*** Killing all processes...

you can the restart that container with

docker start <container ID>

Accessing the container with a bash shell can be done with

docker exec -ti <container ID> /bin/bash

⁠Commands and Environment variables

This is the commands and environment variables used inside nimmis based containers for extra functionality

⁠set_tz

In the default configuration is set to UTC time, if you need it to use the corret time you can change to timezone for the container with this command, syntax is

set_tz <timezone>

To get list of available timezones do

set_tz list

⁠set timezone on startup

Add the environment variable TIMEZONE to the desired timezone, i.e to set timezone to CET Stockhome

docker run -d -e TIMEZONE=Europa/Stockholm nimmis/centos

⁠set timezone in running container

Execute the command on the container as

docker exec -ti <docker ID> set_tz Europa/Stockholm

⁠get list of timezones before starting container

Execute the following command, it will list available timezones and then remove the container

docker run --rm nimmis/centos set_tz list