FIPS (Federal Information Processing Standard) can be enabled (by default or not) on linux kernels to enable the FIPS kernel cryptographic features.
But in some case, this can also lead to some issues with openssl, or any cryptographic tool that you can use within any code.

You can check if FIPS is enabled with that command:

# cat /proc/sys/crypto/fips_enabled
1

If you need to turn this feature off, you will have to first remove any dracut-fips package that you have installed:

# yum -y remove dracut-fips* 

Then, take a backup of the FIPS initramfs and recreate a new file:

# cp -p /boot/initramfs-$(uname -r).img /opt/initramfs-$(uname -r).backup
# dracut -f 

Once the file creation is complete, update your GRUB configuration to disable fips flag and rebuild grub configuration

# perl -pi -e 's/fips=1/fips=0/g' /etc/default/grub 
# grub2-mkconfig -o /boot/grub2/grub.cfg
# grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg

Now, reboot the server and if you check FIPS status again, it should return a value of 0 indicating that FIPS is disabled:

# cat /proc/sys/crypto/fips_enabled
0

When analyzing the output of a bash script, it can be useful to prepend timestamp before each line to see how long it’s taking to do a specific action.

For this, you can use the ‘ts‘ command:

# echo -e "this\nis\na\ntest" | ts '[%Y-%m-%d %H:%M:%S]'
[2019-05-13 09:14:28] this
[2019-05-13 09:14:28] is
[2019-05-13 09:14:28] a
[2019-05-13 09:14:28] test

If the command ‘ts‘ is not available, you might need to install the package moreutils.

Seeing that error in HTTPd/Apache logs when trying to GET some pages?

(13)Permission denied: [client xxxxx]: access to /html/myfile.html denied because search permissions are missing on a component of the path

This is because of some SELinux policies blocking the calls. If you don’t want to turn SELinux off, a simple workaround is:

chcon -R --type=httpd_sys_rw_content_t /html/

When updating or installing a package on a Debian-based distribution, you can face that alert:

W: GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886

This just means that a signing GPG key is missing or expired on your system. The error is giving you the ID of the missing key that you can use for looking for it on the Ubuntu website:

http://keyserver.ubuntu.com:11371/pks/lookup?op=get&search=0xC2518248EEA14886

Copy the key that you just got from the website above into a file – mykey.txt, for example – and import it with the apt-key command:

apt-key add mykey.txt

Try to install/update the package again, and the error should not appear anymore.