Posts Tagged ‘systemctl’

Set all logs to log to to physical console /dev/tty12 (tty12) on Linux

Wednesday, August 12th, 2020

tty linux-logo how to log everything to last console terminal tty12

Those who administer servers from the days of birth of Linux and who used actively GNU / Linux over the years or any other UNIX knows how practical could be to configure logging of all running services / kernel messages / errors and warnings on a physical console.

Traditionally from the days I was learning Linux basics I was shown how to do this on an old Debian Sarge 3.0 Linux without systemd and on all Linux distributions Redhat 9.0 / Calderas and Mandrakes I've used either as a home systems or for servers. I've always configured output of all messages to go to the last easy to access console /dev/tty12 (for those who never use it console switching under Linux plain text console mode is done with key combination of CTRL + ALT + F1 .. F12.

In recent times however with the introduction of systemd pretty much things changed as messages to console are not handled by /etc/inittab which was used to add and refresh physical consoles tty1, tty2 … tty7 (the default added one on Linux were usually 7), but I had to manually include more respawn lines for each console in /etc/inittab.
Nowadays as of year 2020 Linux distros /etc/inittab is no longer there being obsoleted and console print out of INPUT / OUTPUT messages are handled by systemd.
 

1. Enable Physical TTYs from TTY8 till TTY12 etc.


The number of default consoles existing in most Linux distributions I've seen is still from tty1 to tty7. Hence to add more tty consoles and be ready to be able to switch out  not only towards tty7 but towards tty12 once you're connected to the server via a remote ILO (Integrated Lights Out) / IdRAC (Dell Remote Access Controller) / IPMI / IMM (Imtegrated Management Module), you have to do it by telling systemd issuing below systemctl commands:
 

 

 # systemctl enable getty@tty8.service Created symlink /etc/systemd/system/getty.target.wants/getty@tty8.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty9.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty9.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty10.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty10.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty11.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty11.service -> /lib/systemd/system/getty@.service.

systemctl enable getty@tty12.service

Created symlink /etc/systemd/system/getty.target.wants/getty@tty12.service -> /lib/systemd/system/getty@.service.


Once the TTYS tty7 to tty12 are enabled you will be able to switch to this consoles either if you have a physical LCD / CRT monitor or KVM switch connected to the machine mounted on the Rack shelf once you're in the Data Center or will be able to see it once connected remotely via the Management IP Interface (ILO) remote console.
 

2. Taking screenshot of the physical console TTY with fbcat


For example below is a screenshot of the 10th enabled tty10:

tty10-linux-screenshot-fbcat-how-to-screenshot-console

As you can in the screenshot I've used the nice tool fbcat that can be used to make a screenshot of remote console. This is very useful especially if remote access via a SSH client such as PuTTY / MobaXterm is not there but you have only a physical attached monitor access on a DCs that are under a heavy firewall that is preventing anyone to get to the system remotely. For example screenshotting the physical console in case if there is a major hardware failure occurs and you need to dump a hardware error message to a flash drive that will be used to later be handled to technicians to analyize it and exchange the broken server hardware part.

Screenshots of the CLI with fbcat is possible across most Linux distributions where as usual.

In Debian you have to first instal the tool via :
 

# apt install –yes fbcat


and on RedHats / CentOS / Fedoras

# yum install -y fbcat


Taking screenshot once tool is on the server of whatever you have printed on console is as easy as

# fbcat > tty_name.ppm


Note that you might want to convert the .ppm created picture to png with any converter such as imagemagick's convert command or if you have a GUI perhaps with GNU Image Manipulation Tool (GIMP).

3. Enabling every rsyslog handled message to log to Physical TTY12


To make everything such as errors, notices, debug, warning messages  become instantly logging towards above added new /dev/tty12.

Open /etc/rsyslog.conf and to the end of the file append below line :
 

daemon,mail.*;\
   news.=crit;news.=err;news.=notice;\
   *.=debug;*.=info;\
   *.=notice;*.=warn   /dev/tty12


To make rsyslog load its new config restart it:

 

# systemctl status rsyslog

 

 

 

rsyslog.service – System Logging Service
   Loaded: loaded (/lib/systemd/system/rsyslog.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2020-08-10 04:09:36 EEST; 2 days ago
     Docs: man:rsyslogd(8)
           https://www.rsyslog.com/doc/
 Main PID: 671 (rsyslogd)
    Tasks: 4 (limit: 4915)
   Memory: 12.5M
   CGroup: /system.slice/rsyslog.service
           └─671 /usr/sbin/rsyslogd -n -iNONE

 

авг 12 00:00:05 pcfreak rsyslogd[671]:  [origin software="rsyslogd" swVersion="8.1901.0" x-pid="671" x-info="https://www.rsyslo
Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.

 

systemctl restart rsyslog


That's all folks navigate by pressing simultaneously CTRL + ALT + F12 to get to TTY12 or use ALT + LEFT / ALT + RIGHT ARROW (console switch commands) till you get to the console where everything should be now logged.

Enjoy and if you like this article share to tell your sysadmin friends about this nice hack  ! 🙂

 

 

 

How to install GUI on CentOS 7 Minimal and set Gnome Graphical Environment to automatically load on system boot

Wednesday, July 22nd, 2020

centos-linux-logo

I have installed CentOS 7.7 Minimal Server Linux on a VirtualBox Virtual Environment as a test bed machine.

The system got installed easily succesfully with the standard CentOS python based graphical installer, however I needed to place various software which was not there
and for that of course I needed to have a network enabled.

To make network working instead of the default Network NAT configuration for the Virtual Machine I needed to use the Network to be Attached to a Bridged Adapter in order to make
my Windows machine to provide network and (internet) access to VirtualMachine.

virtualbox-virtualmachine-bridged-networking-configuration-screenshot

Then to make networking work after booting into CentOS I had to manually fetch IP via DHCP protocol with command:
 

[root@centos :~]# dhclient enp0s3

 


ethernet0-interface-dhclient-get-ip-linux

To make the setting permanent I had to also of course modify /etc/sysconfig/network-scripts/ifcfg-enp0s3 file and change 

 

ONBOOT=no

 

 

 

to 

ONBOOT=yes


enable-dhclient-centos-linux-shot

On next reboot CentOS boots normally with networking as expected

As by default CentOS Minimal does not provide any graphical environment however I needed to have it in my VM in order to be able to use VboxLinuxAdditions.run (VirtualBox Guest Additions plugins) that enabled the CentOS Operating System to show in Virtualbox in fullscreen and to enable the Copy / Paste buffers to work from The Hypervisor (Windows in that case) and the Guest VM (the CentOS VM).

In CentOS terminology metapackages (a  grouped package under a certain name, alias) are called simply groups) there is a "GNOME Desktop" group that can be used to install the GNOME Graphical Command from that point on with yum, like so:
 

[root@centos :~]# yum -y groups install "GNOME Desktop"


In a while the graphical environment will be in place, the command will install about 1300+ RPM packages, this will take about 5 minutes or so depending on your bandwidth connectivity. Once all is installed and configured succesfully you can use the good old startx command to launch GNOME.

 

 

[root@centos :~]# startx


centos7-linux-graphical-environment-screenshot

This of course will make Xserver and GNOME to run one time and on next reboot, you will end up in a plain text mode environment, so perhaps you will need to make the autolaunch of GNOME environment automatically on each boot in CentOS just like in most modern Linux distributions that use SYSTEMD to handle runlevels, you will need to configure it by changing the systemd default configured target via systemctl:

 

[root@centos :~]# systemctl list-units –type target | egrep "eme|res|gra|mul" 
graphical.target       loaded active active Graphical Interface
multi-user.target      loaded active active Multi-User System

 

[root@centos :~]# systemctl set-default graphical.target
multi-user.target

 

[root@centos :~]# systemctl set-default
graphical.target

 

[root@centos :~]# systemctl set-default graphical.target
graphical.target


Next step was to enable the Guest Additions to do so I had to install in advance 2 RPM packages kernel-headers and kernel-devel


[root@centos :~]# yum install -y kernel-headers kernel-devel

Then I had to mount and run the VboxLinuxAdditions.run script to enable them, i.e.:

 

[root@centos :~]# mkdir /mnt/cdrom
[root@centos :~]# mount /dev/cdrom /mnt/cdrom

[root@centos :~]# cd /mnt/cdrom/
[root@centos :~]# sh VboxLinuxAdditions.run

 


virtualbox-linux-additions-install-screenshot-centos-7-linux