Uly.me

cloud engineer

redhat

Lock a Package in Linux

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Here’s how to lockdown a package to a specific version.

Search for the current package.

$ sudo rpm -qa |  grep sdk
google-cloud-sdk-365.0.1-1.x86_64

Install versionlock.

yum install yum-plugin-versionlock

Lock a package.

yum versionlock google-cloud-sdk-365.0.1-1.x86_64

Display all locked versions.

yum versionlock list

Unlock and clear.

yum versionlock clear

Check Reboot After Updates

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Here’s the command to check if the system needs a reboot after running yum update.

Must be root or run it sudo.

$ needs-restarting -r ; echo $?
Core libraries or services have been updated:
  openssl-libs -> 1:1.0.2k-21.el7_9
  kernel -> 3.10.0-1160.31.1.el7
  dbus -> 1:1.10.24-15.el7
  linux-firmware -> 20200421-80.git78c0348.el7_9
  glibc -> 2.17-324.el7_9
  systemd -> 219-78.el7_9.3
 
Reboot is required to ensure that your system benefits from these updates.
 
More information:
https://access.redhat.com/solutions/27943
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In this instance, it requires a reboot due to a new kernel.

Set Timezone Permanently

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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

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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

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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

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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

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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

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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