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Serial Terminal Configuration in RHEL Distribution

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Serial Terminal Configuration in RHEL 7

Add, or update if already present, the following lines to /etc/default/grub:

GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,115200n8"
GRUB_TERMINAL=serial
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

GRUB_CMDLINE_LINUX_DEFAULT applies this configuration only to the default menu entry, use GRUB_CMDLINE_LINUX to apply it to all the menu entries.
NOTE: each line type above should only appear once within the /etc/default/grub file. If the line already exists, then just modify it rather than add a second copy of same. That is, only one GRUB_CMDLINE_LINUX_DEFAULT line should exist in the file, etc.

Rebuild the /boot/grub2/grub.cfg file by running the grub2-mkconfig -o command as follows:

On BIOS-based machines: ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
On UEFI-based machines: ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Red Hat Enterprise Linux 8

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Reset root password in Centos/Redhat/SL linux

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1. Boot the system and when you see the following message “Press any key to enter the menu”, press any key. (You will see the list of available kernel versions.)

2. Press e in order to edit commands before booting.

3. Highlight the list item with vmlinuz in it by using the arrow keys and press e.

4. Now type single or init 1 at the end of the line.

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Install Varnish on CentOS/RedHat/SL 5 or 6

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Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy. It is installed in front of the web application and it speeds up the web application significantly.

Since varnish is not available in CentOS repo, you have to add the EPEL repo. However Varnish suggests you to add its own repo to always get the latest version.

rpm –nosignature -i http://repo.varnish-cache.org/redhat/varnish-3.0/el5/noarch/varnish-release-3.0-1.noarch.rpm

The –no-signature is only needed on initial installation, since the Varnish GPG key is not yet in the yum keyring

Now lets install varnish

# yum install varnish

Make sure it can handle server reboots 🙂

# chkconfig varnish on

Lets change some parameters to suit our enviornment.

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Reset root Password for Redhat/CentOS/Sl Linux 5.x

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You can log in using single-user mode and create a new root password.

To enter single-user mode, reboot your computer. If you use the default boot loader, GRUB, you can enter single user mode by performing the following:

  1. At the boot loader menu, use the arrow keys to highlight the installation you want to edit and type [A] to enter into append mode.

  2. You are presented with a prompt that looks similar to the following:

    grub append> ro root=LABEL=/

  3. Press the Spacebar once to add a blank space, then add the word single to tell GRUB to boot into single-user Linux mode. The result should look like the following:

    ro root=LABEL=/ single

  4. Press [Enter] and GRUB will boot single-user Linux mode. After it finishes loading, you will be presented with a shell prompt similar to the following:

    sh-2.05b#

  5. You can now change the root password by typing

    passwd root

    You will be asked to re-type the password for verification. Once you are finished, the password will be changed. You can then reboot by typing reboot at the prompt; then you can log in to root as you normally would.

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mod_jk for RHEL6

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If you have a RHEL6 box which ships both Apache and Tomcat6 you might want to connect the two together. You probably have looked around for mod_jk as a RHEL6 RPM or SRPM (src.rpm).

You find that It isn't in EPEL, and it isn't in Red Hat Optional Server 6 RHN channel, etc.

It seems that the new way forward with RHEL/Fedora world is to use mod_proxy_ajp. For example, the RH/Fedora project Spacewalk switched from mod_jk to mod_proxy_ajp.

Note that mod_proxy_ajp is a core module of Apache 2.2 and newer so this should be a rather definitive/final change in recommended connector for Tomcat and Apache.

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