Johnson

To install, remove, and upgrade packages on CentOS, utilize the “yum” package manager by specifying the package name in the terminal.

By default, NTPD uses UDP port 123 for NTP servers and 1023 port for NTP clients. These ports need to open to allow incoming NTP traffic.

The “sudo rm -rf /*” command recursively deletes all files and directories from the root directory. It deletes all the files on the computer permanently.

In Linux, the error “cp: omitting directory” represents that the “cp” command expects a file as the source, not a directory.

To export a GPG private and public key, use the “gpg –export-secret-key -a > prv.key” and “gpg –export -a > pub.key” commands.

To add a DNS server via resolv.conf configuration file, add a nameserver directive followed by the IP address of the DNS server.

To step into, step over, and step out with GDB, use the “step”, “next”, and “finish” commands. These GDB commands quickly identify and fix bugs in the program.

To install and run the TFTP server, execute the “sudo apt install tftpd-hpa” command and configure the “tftpd-hpa” configuration file.

To give full permission to a folder and its subfolders, use the “chmod 777 ” command and hit the “Properties” option by specifying the folder.

To force a clock update using the NTP server, use the “ntpdate” command and “ntpd” service. They synchronize the time on the system with the time NTP server.

To find out which users are in a group within Linux, utilize the “groups”, “getent”, and “id -Gn” commands and the “/etc/group” file.

To reverse SSH tunneling connection, execute the “ssh -R :localhost: @” command.

The difference between cp -r and cp -a is that cp -a preserves all file attributes, while cp -r only preserves the ownership and permissions of the files.

To run the SSH server on a port other than 22 is possible by changing the port number in the “sshd_config” configuration file

To get the file created/creation time in Linux, use the “stat”, “debugfs”, “ls” commands, and “Properties” options in GUI.

To forcefully use wget for a proxy server without modifying system files, set “http_proxy” and “https_proxy” variables with server address and port.

Linux offers the “crontab -l” command to get a list of all scheduled cron jobs. It displays jobs on the basis of monthly, weekly, daily, and hourly.

To install dependencies automatically with the dpkg package manager, users can execute the “sudo apt install -f” command in the terminal.

To unzip the “.tgz” file in the Linux terminal, utilize the “tar”, and “gunzip”, commands. They required the zip file to have the “.tgz” extension.

To generate random strings in Linux, use the “Random Number Generator”, “OpenSSL library”, “UUID generator”, and “mktemp” commands.

The “chmod +x ” command modifies the file permissions and makes it executable. Also, you can make multiple files or directory executables.

To unzip a .gz file without removing the original gzipped file, users can utilize the “gunzip”, “zcat” and “gzip” commands.

To change the password on the root user and user account in Linux, execute the “sudo passwd root” and “sudo passwd ” commands, respectively.

The “firewall-cmd” command displays the firewall rules, allows a specific service, blocks a port, reloads the firewall, gets the firewall zone, and many more.

To set the date through the command line, utilize the “date”, “hwclock”, “timedatectl” and “ntpdate” commands by specifying the “YYYY-MM-DD hh:mm:ss” format.

The “export PATH=something:$PATH” command changes the “PATH” environment variable of the current system by specifying the path in the “something” variable.

To find all large files in the root filesystem, you can utilize the “find”, “du”, and “ncdu” commands. Also, you can specify the size limit, and sorting order.

To see the full log from systemctl status services, execute the “systemctl status service_name -l” command in the system.

Linux offers the “ls” command with “l”, “s”, and “h” options to view the file size along with detail in “long”, “sorting”, and “human-readable” format.

To find the last login on Linux, use the “last”, “lastlog”, “/var/log/auth.log”, “who” and “lastb” commands that display username, terminal, date, and time.

Load average is the measure to determine the processes running or waiting to be run on the CPU. Three different methods can find the load average.

To find and change the MAC address, the ifconfig command, ip command, and “/sys/class/net/*/address” file are used in the system.

The Xmax scan can be performed using the nmap command in the system. This scan displays the status of the ports of the target machine.

The “/dev/null” is a powerful tool in Linux that allows users to discard unwanted data, suppress error messages, make files disappear, and many more.