GNU/Linux users always have love ?Because they can install it from the repositories!
$ love bash: love: command not found... Install package 'love' to provide command 'love'? [N/y] y
That is love is not something appropriate!
#When you do not have the love package installed, you will get the following message $ whatis love love: nothing appropriate.
firewalld (Dynamic Firewall Manager) tool provides a dynamically managed firewall. The tool enables network/firewall zones to define the trust level of network connections and/or interfaces. It has support both for IPv4 and IPv6 firewall settings. Also, it supports Ethernet bridges and allow you to separate between runtime and permanent configuration options. Finally, it supports an interface for services or applications to add firewall rules directly.
To disable firewalld, execute the following command as root or using sudo:
systemctl disable firewalld;
To enable firewalld, execute the following command as root or using sudo:
systemctl enable firewalld;
To stop (or deactivate) firewalld,execute the following command as root or using sudo:
systemctl stop firewalld;
To start (or activate) firewalld, execute the following command as root or using sudo:
systemctl start firewalld;
To check the status of firewalld, execute the following command as root or using sudo:
systemctl status firewalld;
systemd provides a dependency system between various entities called “units” of 12 different types. Units encapsulate various objects that are relevant for system boot-up and maintenance. The majority of units are configured in unit configuration files, whose syntax and basic set of options is described in systemd.unit(5), however some are created automatically from other configuration, dynamically from system state or programmatically at runtime. Units may be “active” (meaning started, bound, plugged in, …, depending on the unit type, see below), or “inactive” (meaning stopped, unbound, unplugged, …), as well as in the process of being activated or deactivated, i.e. between the two states (these states are called “activating”, “deactivating”). A special “failed” state is available as well, which is very similar to “inactive” and is entered when the service failed in some way (process returned error code on exit, or crashed, or an operation timed out). If this state is entered, the cause will be logged, for later reference. Note that the various unit types may have a number of additional substates, which are mapped to the five generalized unit states described here.
— From man systemd
The above, in a nutshell:
enabled is a service that is configured to start when the system bootsdisabled is a service that is configured to not start when the system bootsactive is a service that is currently runninginactive is a service that is currently stopped and may be disabled, but it can be started and become activefirewalld (Dynamic Firewall Manager) tool provides a dynamically managed firewall. The tool enables network/firewall zones to define the trust level of network connections and/or interfaces. It has support both for IPv4 and IPv6 firewall settings. Also, it supports Ethernet bridges and allow you to separate between runtime and permanent configuration options. Finally, it supports an interface for services or applications to add firewall rules directly.
To disable firewalld, execute the following command as root or using sudo:
systemctl disable firewalld
To enable firewalld, execute the following command as root or using sudo:
systemctl enable firewalld
To stop (or deactivate) firewalld,execute the following command as root or using sudo:
systemctl stop firewalld
To start (or activate) firewalld, execute the following command as root or using sudo:
systemctl start firewalld
To check the status of firewalld, execute the following command as root or using sudo:
systemctl status firewalld
systemd provides a dependency system between various entities called “units” of 12 different types. Units encapsulate various objects that are relevant for system boot-up and maintenance. The majority of units are configured in unit configuration files, whose syntax and basic set of options is described in systemd.unit(5), however some are created automatically from other configuration, dynamically from system state or programmatically at runtime. Units may be “active” (meaning started, bound, plugged in, …, depending on the unit type, see below), or “inactive” (meaning stopped, unbound, unplugged, …), as well as in the process of being activated or deactivated, i.e. between the two states (these states are called “activating”, “deactivating”). A special “failed” state is available as well, which is very similar to “inactive” and is entered when the service failed in some way (process returned error code on exit, or crashed, or an operation timed out). If this state is entered, the cause will be logged, for later reference. Note that the various unit types may have a number of additional substates, which are mapped to the five generalized unit states described here.
— From man systemd
The above, in a nutshell:
enabled is a service that is configured to start when the system bootsdisabled is a service that is configured to not start when the system bootsactive is a service that is currently runninginactive is a service that is currently stopped and may be disabled, but it can be started and become activeThe following methods demonstrate different methods on how to compute the time a potion of code or script take to complete their execution.
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The following example will calculate the execution time in seconds by subtracting the system date and time in seconds since 1970-01-01 00:00:00 UTC once right before the script goes to the computation part and once right after.
In order to get the system date and time in seconds since 1970-01-01 00:00:00 UTC we use the command date +%s.
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#!/bin/bash #Print the system date and time in seconds since 1970-01-01 00:00:00 UTC startTime=$(date +%s); #We pick a random number between 1 and 10. #Then we delay the execution for that amount of seconds. sleep $(( (RANDOM % 10) + 1 )); endTime=$(date +%s); #Subtract endTime from startTime to get the total execution time totalTime=$(($endTime-$startTime)); echo "Process finished after $totalTime seconds"; exit 0;
The following example will calculate the execution time in seconds by reseting the bash internal variable SECONDS to 0, forcing the shell to continue counting from there.
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#!/bin/bash #This variable expands to the number of seconds since the shell was started. #We set it to 0, forcing the shell to continue counting from there. SECONDS=0; #We pick a random number between 1 and 10. #Then we delay the execution for that amount of seconds. sleep $(( (RANDOM % 10) + 1 )); echo "Process finished after $SECONDS seconds"; exit 0;
The following example uses the bash time command, which reports the time consumed by a pipeline’s execution.
When time command is executed without its complete path, then the bash built-in time command is executed, instead of the GNU time command. We will use the bash time command in this example and we will use it to run a whole block of commands.
Please note that time command will return the time in seconds as a float (i.e. there will be decimal places. e.g. 1 will be printed as 1.00).
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#!/bin/bash #The bash time command reports the time consumed by pipeline's execution #When time command is executed without its complete path, then the bash built-in time command is executed, instead of the GNU time command. #We will use the bash time command in this example and we will use it to run a whole block of commands. #We change the output format of time to print elapsed real time in seconds. TIMEFORMAT="%E"; #We pick a random number between 1 and 10. #Then we delay the execution for that amount of seconds. totalTime=`time ( sleep $(( (RANDOM % 10) + 1 )) ) 2>&1`; #Please note that time command will return the time in seconds as a float (i.e. there will be decimal places. e.g. 1 will be printed as 1.00). #This will happen as time has build-in more precision than the first two methods presented here. echo "Process finished after $totalTime seconds"; totalTimeBlock=`time ( sleep $(( (RANDOM % 10) + 1 )); sleep $(( (RANDOM % 10) + 1 )); ) 2>&1`; echo "Block finished after $totalTimeBlock seconds"; exit 0;
The GNU time command runs the specified program command with the given arguments.
When time command is executed without its complete path (in our case it was /usr/bin/time), then the bash built-in time command is executed, instead of the GNU time command. To make sure we use the GNU time command, we use which to get the full path of the time command.
Please note that time command will return the time in seconds as a float (i.e. there will be decimal places. e.g. 1 will be printed as 1.00).
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#!/bin/bash #The time command runs the specified program command with the given arguments. #When time command is executed without its complete path (in our case it was /usr/bin/time), then the bash built-in time command is executed, instead of the GNU time command. #To make sure we use the GNU time command, we use which to get the full path of the time command. time=`which time`; #We pick a random number between 1 and 10. #Then we delay the execution for that amount of seconds. #We change the output format of time to print elapsed real time in seconds. totalTime="$( $time -f '%e' sleep $(( (RANDOM % 10) + 1 )) 2>&1 1>/dev/null )"; #Please note that time command will return the time in seconds as a float (i.e. there will be decimal places. e.g. 1 will be printed as 1.00). #This will happen as time has build-in more precision than the first two methods presented here. echo "Process finished after $totalTime seconds"; exit 0;
Each time RANDOM internal variable is referenced, a random integer between 0 and 32767 is generated.
By using the RANDOM variable in this command $(( (RANDOM % 10) + 1 )); we perform a modulo on the random value with the static value 10. This way we force the range of valid values to be between 0 and 9.
Later, we add 1 to that value to shift the range to be between 1 and 10.
