If you get the following error when trying to execute a sudo command, despite the fact that you configured your sudoers or sudoers.d config file properly:

sudo: pam_unix(sudo:auth): conversation failed
sudo: pam_unix(sudo:auth): auth could not identify password for [user]

Then, you might need to have a look at the PAM configuration on your device.
Ensure that you have this line enabled in your /etc/pam.d/sudo file:

# cat /etc/pam.d/sudo
#%PAM-1.0
# The line below should fix the sudo:auth could not identify password
auth       sufficient   pam_permit.so

# The lines below are the default config
auth       include      system-auth
account    include      system-auth
password   include      system-auth
session    optional     pam_keyinit.so revoke

session    include      system-auth

Once you changed this file, no need to restart anything – just retry your command and it should work!

If you want to filter some specific logs and redirect them to another server or to another file, you can use the module provided with rsyslog called “omprog”.

Thanks to that module, you can just ask rsyslog to execute a script on every logs you have from a specific application and process it with your own rules.

Let’s go with a simple example, I want to filter my logs from postfix and only extract few specific information.

Below is the configuration I will now push to /etc/rsyslog.d/rsyslog_postfix.conf in order to:

1. Redirect the current log to /var/log/maillog as a default path (to keep the raw log)
2. Process every log line with my python script in order to extract only some specific informations that I will write in /var/log/rsyslog_postfix.log

module(load="omprog")

mail.* {
    action(type="omfile" 
        file="/var/log/maillog")
    action(type="omprog"
        name="rsyslog_postfix"
        binary="/usr/bin/python3 /opt/rsyslog_postfix.py"
        queue.type="LinkedList"
        queue.size="20000"
        queue.saveOnShutdown="on"
        queue.workerThreads="4"
        queue.workerThreadMinimumMessages="5000"
        action.resumeInterval="5"
        output="/var/log/rsyslog_postfix.log")
    stop
}

Rsyslog script

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# python_version  :3.6
#===========================

import sys
import traceback
import datetime

if __name__ == '__main__':
    data = {}
    while True:
        try:
            line = sys.stdin.readline()
            msg = line.strip()
            if msg != "":
                data.clear()
                timestamp = msg.split(' ')[0]
                proc= msg.split(' ')[2].split('[')[0]
                pid = msg.split(' ')[2].split('[')[1].split(']')[0]
                log = msg.split(' ', 3)[3]
                if proc.startswith("postfix/"):
                    data = { 
                        "Timestamp": timestamp,
                        "Process": proc,
                        "PID": pid,
                    }
                    data["PostfixID"] = log.split(' ')[0].split(':')[0]
                print(data)
        except Exception as e:
            err = traceback.format_exc()
            print(err)

Now, I just need to restart rsyslogd process and the logs will start to be processed as expected, and you should get the raw logs in /var/log/maillog and the filtered ones in /var/log/rsyslog_postfix.log

systemctl restart rsyslog

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.