Simply adjust / sync your server’s clock in case you get the following error message while using aws-cli – “AWS was not able to validate the provided access credentials”

Use the following command to clear you cached memory:

root@linux [~]# echo 1 > /proc/sys/vm/drop_caches

In case you receive the mentioned error while trying to install rmagick then simply issue the following:

# yum install ImageMagick-devel

Once ImageMagick-devel is installed then you can retry installing rmagick using:

# gem install rmagick

Here’s how to fix the following Postfix issue:

send-mail: warning: inet_protocols: IPv6 support is disabled: Address family not supported by protocol
send-mail: warning: inet_protocols: configuring for IPv4 support only
postdrop: warning: inet_protocols: IPv6 support is disabled: Address family not supported by protocol
postdrop: warning: inet_protocols: configuring for IPv4 support only

# /usr/sbin/postconf | grep inet_protocols
inet_protocols = all

# vi /etc/postfix/main.cf

Search for: inet_protocols and change it from “inet_protocols = all” to “inet_protocols = ipv4”
Save /etc/postfix/main.cf and and restart Postfix service:

# /etc/init.d/postfix restart