Uly.me

cloud engineer

redhat

Set Timezone Permanently

by ·

It’s recommended to set the clock to UTC. In rare occasions, local time may be needed.

Here’s how to set your server’s timezone permanently.

Check the date first.

date

Backup localtime. Set it to US Eastern Time.

mv /etc/localtime /etc/localtime.backup
ln -s /usr/share/zoneinfo/America/New_York /etc/localtime

Backup clock. Set it to US Eastern Time.

cp -p /etc/sysconfig/clock /etc/sysconfig/clock.backup 
> /etc/sysconfig/clock
echo ZONE=\"America/New_York\" > /etc/sysconfig/clock

Run the date again to validate.

date

Install OpenJDK 8

by ·

Here’s the installation instructions for OpenJDK 8.

For Fedora, Redhat and Oracle Linux.

yum install java-1.8.0-openjdk

For Debian and Ubuntu.

apt-get install openjdk-8-jre

To see if the packages (symbolic links) are there, they can be found in /etc/alternatives/, at least in Redhat 7.

ls -l /etc/alternatives/

HTTPD on Redhat & Centos

by ·

Here are the commands to start, stop, enable and get the status of Apache on RHEL and CentOS.

systemctl enable httpd  # enable on bootup
systemctl status httpd  # get status
systemctl start httpd   # start
systemctl stop httpd    # stop
systemctl restart httpd # restart

OpenSSL Upgrade

by ·

Here’s how to upgrade to OpenSSL 1.1 on Redhat/Centos.

# check
openssl version
yum info openssl
# download and install
cd /usr/local/src
wget https://www.openssl.org/source/openssl-1.0.2-latest.tar.gz
tar -zxf openssl-1.0.2-latest.tar.gz
# compile
cd openssl-1.0.2a
./config
make
make test
make install
# update softlink
mv /usr/bin/openssl /root/
ln -s /usr/local/ssl/bin/openssl /usr/bin/openssl
# verify new version
openssl version

Yum Repo Plugins

by ·

Here’s how to disable plugin in Yum repos.

# check which plugins are enabled
yum repolist
# disable plugins
yum update --disableplugin=product-id,subscription-manager
# check agin
yum repolist

If that doesn’t work, check the individual config files of each plugin.

cd /etc/yum/pluginconf.d/
vim product-id.conf
vim subscription-manager.conf

Disable it.

[main]
enable=0

Create Swap Disk

by ·

To see which disk is available for swap disk use.

lsblk
blkid
df -Th

Format the disk.

fdisk /dev/xvda

Create a swap disk.

sudo mkswap -f /dev/xvda
sudo swapon -s /dev/xvda
# or
sudo swapon /dev/xvda

Check if swap disk is available.

lsblk
free -h 
cat /proc/swaps
cat /proc/meminfo
swapon -s
top
vmstat
vmstat 1 5

Apache & Webroot

by ·

Where’s Apache and webroot for the different distros?

Webroot:

# Redhat, Fedora, Centos, Amazon Linux
/var/www/html
# Debian, Ubuntu, Mint
/var/www/html

Apache Configuration:

# Redhat, Fedora, Centos, Amazon Linux
/etc/httpd/conf/httpd.conf
# Debian, Ubuntu, Mint
/etc/apache2/sites-available/default

Yum Remove Repo

by ·

How to remove repos in Yum. Just delete the repo file in /etc/yum.repos.d.

rm /etc/yum.repos.d/repo-name.repo

ReiserFS

by ·

Install ReiserFS

rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
rpm -Uvh https://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm
yum update
yum install kmod-reiserfs kmod-reiserfs

Make a ReiserFS

fdisk /dev/xvdf
n, p, 1
[return]
[return]
mkreiserfs /dev/xvdf1
mount -t reiserfs /dev/xvdf1 /data

Other Reiserfs commands

reiserfsck /dev/xvdf1
resize_reiserfs /dev/xvdf1