Linux

It is a command using which we can do low level logical volume management. So basically dmsetup is used to manage logical devices that use the device-mapper driver. The first argument to dmsetup is a command. The second argument is the logical device name or uuid. The package which provides dmsetup command can be found out using: # yum whatprovices /sbin/dmsetup ... 7:device-mapper-1.02.158-2.el7_7.2.x86_64 : Device mapper utility Repo : @updates Matched from: Filename : … [Read more...] about Examples of using dmsetup command in Linux

The seq command prints a sequence of integers or real numbers, suitable for piping to other programs. The seq command can come in handy in various other commands and loops to generate sequence of numbers. The Syntax The general syntax of the "seq" command is: # seq [options] specification The examples 1. To simply print a sequence of number starting from a 1, use the below command: # seq 4 1 2 3 4 By default, seq command starts printing the sequence of numbers from 1, if not … [Read more...] about Linux “seq” Command Examples

Question: How can we restrict user/group access to a system using ssh? SSH uses specific files for configuration to achieve these various restrictions. Inbound ssh sessions (into the host) are handled by sshd (the ssh daemon). This process has its own configuration file, /etc/ssh/sshd_config. The parameters in the /etc/ssh/sshd_config file that apply are AllowGroups, AllowUsers, DenyGroups, and DenyUsers. If these parameters are set, it will affect all users from all hosts. To restrict … [Read more...] about How to Configure SSH to restrict Users/Groups with allow and deny directives

Question: How can we allow a user with empty password to login to a Linux system? Although it seems a risky requirement, but sometimes in a private, development environment this can come handy. Also openssh provides you with an option to have empty passwords for users while doing ssh. From the man page of sshd_config: # man sshd_config ... PermitEmptyPasswords When password authentication is allowed, it specifies whether the server allows login to accounts with empty … [Read more...] about How to allow ssh with empty passwords in Linux

To run more that one command simultaneously we can use the & (ampersand) special character. Another use of & is running the commands in the background. In that case though, you should use & once and the end of the command or script. For example: # [some command or script] & Using & (ampersand) to run commands simultaneously In order to run 2 commands simultaneously use the & special character between the 2 or more commands. The syntax is: # command1 & command2 & command3 .. For example, … [Read more...] about What is the difference between & (ampersand) and && (double ampersand) while executing simultaneous commands on Linux

What is an exit code Every script, command, or binary exits with a return code. You can see this value in the special variable $?. Return codes are numeric and are limited to being between 0-255 because an unsigned 8-bit integer is used. If you use a value of -1, it will return 255. Each execution terminates with an exit code, whether successful or not, with an error message or silently. For example: $ date ; echo $? Sat Jan 18 08:06:07 IST 2020 0 As you can see, the exit code is 0 … [Read more...] about What are Bash Exit Codes in Linux