I would like to search and find all files which contain a word called “main()” for all directories located in $HOME/project/school. How do I use the grep command to find text including all subdirs under Unix or Linux operating systems?


Many users are using ssh to log into a remote machine and append the indicated identity file to machine’s ~/.ssh/authorized_keys file. I recently moved one of my server, and I would like to revoke openssh keys and disable user access under Linux operating systems. How do I revoke OpenSSH keys under Unix or Linux operating systems?


I see many examples and man pages on how to do operations like search-and-replace using sed. But, I want to match a given string or a regular pattern expression and display on the screen. How do I print lines with matching pattern using sed command only under Unix like operating systems?


I own a Linux powered Synology dedicated Network Attached Storage (NAS) server for my home office use. How do I run fsck on Synology DiskStation that offers RAID storage using Linux command line options over an ssh session?


What is the maximum character length of arguments in a shell command? How do I find out the maximum length of arguments for a new process under Linux or Unix like operating systems?


How do I find out my DNS server IP address assiged my my ISP under Unix or Linux operating system using command prompt? How do I find preferred dns server under Debian / Ubuntu / Fedora Linux desktop system?


I‘m trying to install latest version of Hewlett-Packard’s Linux Imaging and Printing software (HPLIP) for my office jet printer. In order to install latest version of HPLIP I removed the hplip-gui, hplip, hplip-cups, hplip-data, hpijs, and hpijs-ppds Debian Linux packages However, I’m getting the following error:

Debian warning: CUPSEXT could not be loaded. Please check HPLIP installation.

How do I fix this error while installing under Debian Linux 6.0.5 amd64 bit?