Rearrange with linux sort command
One of the best ways to order the contents of a file or an output is to use the Linux sort command instead of making a script to do so and save administration time. The sort command is one of…
Tag Unix
OCSP and CRL certificate validation with openssl
In this post I’m going to explain two of the openssl options to perform a certificate validation and determine whether it is revoked or not. But before jumping to the topic, let’s briefly review some PKI (Public Key Infrastructure) fundamentals.…
Display currently running processes in tree format with pstree Linux command
The pstree command works similarly to ps since it lists the current running processes in the Linux system but in a more graphical way. Is not a typical command, but it might be interesting to know about it since it…
Counting lines words or characters with Linux wc command
Linux provides many commands, that can be used for many different purposes and situations, to either obtain information quickly or to solve any problem with a script. One of them serves for counting lines, words or characters in a file…
List running processes with Linux ps command
Here’s another useful Linux command, the ps, that will show which processes are running in the system to troubleshoot, audit, forensics and so on. Since it is commonly used for these purposes, the recommendation is to get familiar with it…
Using cut Linux command to process a formatted file or output
The cut Linux command is a useful tool to extract the desired data from a delimited format file or output like csv, xml or json. Normally, depending on the type of file, it needs some preprocessing before gathering successfully the…
See the first lines of a file with Linux head command
When you troubleshoot or audit a system by handling its log files, it might be useful to get the first lines of them in order to know, the timestamp or date of when the file was created or newly rotated,…
Viewing files or logs with Linux less command
One of my favourite Linux commands is less which is also the one that I use the most when the troubleshooting activities needs to review some sort of logs, config files, audit files and so on. Thanks to this great…
How to encrypt files with symmetric key using openssl
The symmetric encryption is the most used cryptographic operation to protect the confidentiality of the information whether it is personal information or corporate sensitive data. The main reason why symmetric encryption is preferred in most of the cases instead of…
How to locate files and directories easily with Linux mlocate
In this post it will describe the locate command, which is a great tool to search files and directories in the system. This command does not work alone and needs to be helped by another one called updatedb used to…
How to create files or modify file metadata with Linux touch command
The touch is one of the most basic Linux commands for empty file creation and for changing the file metadata timestamps. You normally don’t need to install it specifically because it comes with the Linux system. The touch syntax command…
grep the most used Linux command for searching text patterns in files
This basic command it’s one of the most used when working with a Linux shell which brings a lot of powerful options to search text like the use of regular expressions. So in this post, it will be explained how…