Silviu Mocanu

Linux: Using screen and screen under su    If you need to run something and let is run after you close the session, you can use screen. Install the screen package and just run screen. You can de-attach from the screen shell, using the "CTRL+A" keyboard shortcut.   To list the screen sessions, you can run "screen -ls" command: debian:~# screen -ls There are screens on:         14573.pts-1.debian       (03/27/2019 06:59:01 PM)        (Attached)         14546.pts-1.debian       (03/27/2019 06:58:55 PM)        (Detached) To re-attach to a screen session you can run "screen -r {session name}":  debian:~# screen -r 14573.pts-1.debian In order to attach to the same screen session from different shells, you need to use the "-xr" arguments, enabling multi-display mode.  debian:~# screen -xr 14573.pts-1.debian When you need to run it un...

Working with sed (a stream editor)   At some point I had to modify the configuration of multiple nginx configuration files, replacing on all of them a specific string with another one, commenting some strings, deleting some other strings, on one of my CentOS machines.   If I would go to edit manually file by file, it would take a few hours, at least.   So, I choose to use sed and to edit all files at the same time and in order to explain, I creates 100 files containing the same string, I'm using "tee" command: johnyc20@centos:~$ echo "fastcgi_pass 127.0.0.1:9501;"  | tee site-name-{1..100}.conf   Now I have 100 files containg the "fastcgi_pass 127.0.0.1:9501;": johnyc20@centos:~$ cat site-name-* fastcgi_pass          127.0.0.1:9501;   Now I will explain: How to replace content How to comment lines How to insert lines  How to delete lines Short summary of sed options How to replace content The firs...

One of the preferred method of authentication on network devices is using SSH with a SSH public key. In order to be able to authenticate yourself, you have to generate a SSH key pair. A SSH key is composed of two parts, one private key (which should remain "private" and also should be password protected ) and one public key which should be installed on the SSH server in order to authenticate you. SSH client on Linux: In order to generate a SSH key pair on Linux, you will need to use "ssh-keygen" tool, which is a part of the "openssh-client" package on Debian-like operating systems: smocanu@debian7:~$ dpkg -S $(which ssh-keygen) openssh-client: /usr/bin/ssh-keygen or a part of "openssh" package on RedHat-like operating systems: smocanu@centos6 ~$ rpm -qf $(which ssh-keygen) openssh-5.3p1-94.el6.x86_64 The generating process is quite simple, just run the "ssh-keygen" command, and it will ask you the location of the new key ...

If you have to enable secure connections to your service(s), you will need to buy a certificate or generate a self signed certificate for it. If you have to buy one, you have to generate a private certificate and a certificate request. If you will use a self signed certificate, you will need to generate a private, a request and a public certificate. You can do that by using the ' openssl ' tool. First at all, you have to generate a password, I'm usually using ' apg ': smocanu@debian7:~$ apg -n1 -m8 -x8 -t tiWiejTo (ti-Wiej-To) After that we are ready to generate the private certificate, this one should be kept safely, no one else should have it. I'm generating a 512bits RSA certificate: smocanu@debian7:~$ openssl genrsa -des3 -out ss.example.com.key 512 Generating RSA private key, 512 bit long modulus ........................++++++++++++ ...................++++++++++++ e is 65537 (0x10001) Enter pass phrase for ss.example.com.key: Verifying - Ent...