In this tutorial, we will show you how to use the&nbsp;<code>shutdown</code>&nbsp;command through practical examples and detailed explanations of the most common&nbsp;<code>shutdown</code>&nbsp;options.



The&nbsp;<code>shutdown</code>&nbsp;command brings the system down in a secure way. When the&nbsp;<code>shutdown</code>&nbsp;is initiated, all logged-in users and processes are notified that the system is going down, and no further logins are allowed. You can shut down your system immediately or at the specified time.



<h2 id="shutdown-command-syntax">Shutdown Command Syntax</h2>



Before going into how to use the&nbsp;<code>shutdown</code>&nbsp;command, let’s start by reviewing the basic syntax.



The&nbsp;<code>shutdown</code>&nbsp;command expressions take the following form:



<pre class="wp-block-code"><code>shutdown &#91;OPTIONS] &#91;TIME] &#91;MESSAGE]</code></pre>



<ul><li><code>options</code>&nbsp;-&nbsp;<a href="http://man7.org/linux/man-pages/man8/shutdown.8.html" target="_blank" rel="noreferrer noopener nofollow">Shutdown options</a>&nbsp;such as halt, power-off (the default option) or reboot the system.</li><li><code>time</code>&nbsp;- The time argument specifies when to perform the shutdown process.</li><li><code>message</code>&nbsp;- The message argument specifies a message which will be broadcast to all users.</li></ul>



On the recent Linux distributions&nbsp;<code>shutdown</code>&nbsp;is an alias to&nbsp;<code>systemctl</code>&nbsp;and it is available in the system only for compatibility reasons.



<h2 id="how-to-use-the-shutdown-command">How to Use the&nbsp;<code>shutdown</code>&nbsp;Command</h2>



Only the root and users with&nbsp;<code>sudo</code>&nbsp;privileges can use&nbsp;<code>crontab</code>&nbsp;command.



When used with no arguments, the&nbsp;<code>shutdown</code>&nbsp;command will power off the machine.



<pre class="wp-block-code"><code>sudo shutdown</code></pre>



<figure class="wp-block-image size-large"><img src="http://ec2-13-127-91-65.ap-south-1.compute.amazonaws.com/wp-content/uploads/2020/12/shutdown.jpg" alt="" class="wp-image-763"/></figure>



The shutdown process starts after 1 minute, which is the default time interval.



<h2 id="how-to-shutdown-the-system-at-a-specified-time">How to Shutdown the System at a Specified Time</h2>



The time argument can have two different formats. It can be an absolute time in the format&nbsp;<code>hh:mm</code>&nbsp;and relative time in the format&nbsp;<code>+m</code>&nbsp;where m is the number of minutes from now.



The following example will schedule system shutdown at 11 A.M:



<pre class="wp-block-code"><code>sudo shutdown 11:00</code></pre>



The following example will schedule system&nbsp;<code>shutdown</code>&nbsp;in 10 minutes from now:



<pre class="wp-block-code"><code>sudo shutdown +10</code></pre>



<h2 id="how-to-shutdown-the-system-immediately">How to Shutdown the System Immediately</h2>



To shut down your system immediately you can use&nbsp;<code>+0</code>&nbsp;or its alias&nbsp;<code>now</code>:



<pre class="wp-block-code"><code>sudo shutdown now</code></pre>



<h2 id="how-to-broadcast-a-custom-message">How to Broadcast a Custom Message</h2>



To broadcast a custom message along with the standard&nbsp;<code>shutdown</code>&nbsp;notification type your message after the time argument.



The following example, will shut down the system in 30 minutes from now and notify the users that a hardware upgrade will be performed:



<pre class="wp-block-code"><code>sudo shutdown +30 "Hardware upgrade"</code></pre>



It is important to mention that when specifying a custom wall message, you must specify a time argument too.



<h2 id="how-to-reboot-the-system">How to Reboot the System</h2>



To reboot the system, use the&nbsp;<code>-r</code>&nbsp;argument:



<pre class="wp-block-code"><code>sudo shutdown -r</code></pre>



You can also specify a time argument and a custom message:



<pre class="wp-block-code"><code>shutdown -r +5 "Updating kernel"</code></pre>



The command above will reboot the system after 5 minutes and broadcast&nbsp;<code>Updating kernel</code>.



<h2 id="how-to-cancel-a-scheduled-shutdown">How to Cancel a Scheduled Shutdown</h2>



If you have scheduled shutdown and you want to cancel it, you can use the&nbsp;<code>-c</code>&nbsp;argument:



<pre class="wp-block-code"><code>sudo shutdown -c</code></pre>



When canceling a scheduled shutdown, you cannot specify a time argument, but you can still broadcast a message that will be sent to all users.



<pre class="wp-block-code"><code>sudo shutdown -c "Canceling the reboot"</code></pre>



<h2 id="conclusion">Conclusion</h2>



The&nbsp;<code>shutdown</code>&nbsp;command allows you to halt, power-off and reboot your Linux system.



To learn more about&nbsp;<code>shutdown</code>, visit the&nbsp;<a href="https://linux.die.net/man/8/shutdown" rel="noreferrer noopener" target="_blank">shutdown man</a>&nbsp;page.



If you have any questions or feedback, feel free to leave a comment.

In this tutorial, we will show you how to use the&nbsp;shutdown&nbsp;command through practical examples and detailed explanations of the most com...

Linux Shutdown Command - TCMHACK

Linux Shutdown Command

New Linux converts coming from the Windows world may find working with the command line to be somewhat intimidating. However, it's not that diffi...

Basic & Useful Linux Commands - TCMHACK

Basic & Useful Linux Commands

<h2>Name</h2>



Crontab - files used to schedule the execution of programs



<h2>Description</h2>



A crontab file contains instructions for the cron daemon in the following simplified manner: "run this command at this time on this date". Each user can define their own crontab. Commands defined in any given crontab are executed under the user who owns that particular crontab. Uucp and News usually have their own crontabs, eliminating the need for explicitly running su as part of a cron command.



Blank lines, leading spaces, and tabs are ignored. Lines whose first non-white space character is a pound-sign (#) are comments, and are not processed. Note that comments are not allowed on the same line as cron commands, since they are considered a part of the command. Similarly, comments are not allowed on the same line as environment variable settings.



An active line in a crontab is either an environment setting or a cron command. An environment setting is of the form:



<pre class="wp-block-preformatted">name = value</pre>



where the white spaces around the equal-sign (=) are optional, and any subsequent non-leading white spaces in value is a part of the value assigned to name. The value string may be placed in quotes (single or double, but matching) to preserve leading or trailing white spaces.



Several environment variables are set up automatically by the cron daemon. SHELL is set to /bin/sh, and LOGNAME and HOME are set from the /etc/passwd line of the crontab´s owner. HOME and SHELL can be overridden by settings in the crontab; LOGNAME can not.



(Note: the LOGNAME variable is sometimes called USER on BSD systems and is also automatically set).



In addition to LOGNAME, HOME, and SHELL, cron looks at the MAILTO variable if a mail needs to be send as a result of running any commands in that particular crontab. If MAILTO is defined (and non-empty), mail is sent to the specified address. If MAILTO is defined but empty (MAILTO=""), no mail is sent. Otherwise, mail is sent to the owner of the crontab. This option is useful if you decide to use /bin/mail instead of /usr/lib/sendmail as your mailer. Note that /bin/mail does not provide aliasing and UUCP usually does not read its mail. If MAILFROM is defined (and non-empty), it is used as the envelope sender address, otherwise, ``root'' is used.



By default, cron sends a mail using the 'Content-Type:' header of 'text/plain' with the 'charset=' parameter set to the 'charmap/codeset' of the locale in which crond is started up, i.e., either the default system locale, if no LC_* environment variables are set, or the locale specified by the LC_* environment variables. Different character encodings can be used for mailing cron job outputs by setting the CONTENT_TYPE and CONTENT_TRANSFER_ENCODING variables in a crontab to the correct values of the mail headers of those names.



The CRON_TZ variable specifies the time zone specific for the cron table. The user should enter a time according to the specified time zone into the table. The time used for writing into a log file is taken from the local time zone, where the daemon is running.



The MLS_LEVEL environment variable provides support for multiple per-job SELinux security contexts in the same crontab. By default, cron jobs execute with the default SELinux security context of the user that created the crontab file. When using multiple security levels and roles, this may not be sufficient, because the same user may be running in different roles or in different security levels.



The RANDOM_DELAY variable allows delaying job startups by random amount of minutes with upper limit specified by the variable. The random scaling factor is determined during the cron daemon startup so it remains constant for the whole run time of the daemon.



The time and date fields are:



<pre class="wp-block-code"><code>field allowed values
----- --------------
minute 0-59
hour 0-23
day of month 1-31
month 1-12 (or names, see below)
day of week 0-7 (0 or 7 is Sunday, or use names)</code></pre>



A field may contain an asterisk (*), which always stands for "first-last".



Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. The specified range is inclusive. For example, 8-11 for an 'hours' entry specifies execution at hours 8, 9, 10, and 11. The first number must be less than or equal to the second one.



Lists are allowed. A list is a set of numbers (or ranges) separated by commas. Examples: "1,2,5,9", "0-4,8-12".



<h2>EXAMPLE CRON FILE </h2>



<pre class="wp-block-code"><code># use /bin/sh to run commands, no matter what /etc/passwd says
SHELL=/bin/sh
# mail any output to `paul', no matter whose crontab this is
MAILTO=paul
#
CRON_TZ=Japan
# run five minutes after midnight, every day
5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&amp;1
# run at 2:15pm on the first of every month -- output mailed to paul
15 14 1 * * $HOME/bin/monthly
# run at 10 pm on weekdays, annoy Joe
0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
5 4 * * sun echo "run at 5 after 4 every sunday"</code></pre>



<h2>Jobs in /etc/cron.d/</h2>



The jobs in cron.d and /etc/crontab are system jobs, which are used usually for more than one user, thus, additionally the username is needed. MAILTO on the first line is optional.



<h2>EXAMPLE OF A JOB IN /etc/cron.d/job</h2>



<pre class="wp-block-code"><code>#login as root
#create job with preferred editor (e.g. vim)
MAILTO=root
* * * * * root touch /tmp/file</code></pre>



<h2>SELinux with multi level security (MLS)</h2>



In a crontab, it is important to specify a security level by crontab -s or specifying the required level on the first line of the crontab. Each level is specified in /etc/selinux/targeted/seusers. When using crontab in the MLS mode, it is especially important to:



<ul><li>check/change the actual role,</li><li>set correct role for directory, which is used for input/output.</li></ul>



<h2>EXAMPLE FOR SELINUX MLS</h2>



<pre class="wp-block-code"><code># login as root
newrole -r sysadm_r
mkdir /tmp/SystemHigh
chcon -l SystemHigh /tmp/SystemHigh
crontab -e
# write in crontab file
MLS_LEVEL=SystemHigh
0-59 * * * * id -Z > /tmp/SystemHigh/crontest</code></pre>



<h2>FILES</h2>



<ul><li>/etc/crontab main system crontab file.</li><li>/var/spool/cron/ a directory for storing crontabs defined by users.</li><li>/etc/cron.d/ a directory for storing system crontabs.</li></ul>



<h2>EXTENSIONS</h2>



These special time specification "nicknames" which replace the 5 initial time and date fields, and are prefixed with the '@' character, are supported:



<pre class="wp-block-code"><code>@reboot : Run once after reboot.
@yearly : Run once a year, ie. "0 0 1 1 *".
@annually : Run once a year, ie. "0 0 1 1 *".
@monthly : Run once a month, ie. "0 0 1 * *".
@weekly : Run once a week, ie. "0 0 * * 0".
@daily : Run once a day, ie. "0 0 * * *".
@hourly : Run once an hour, ie. "0 * * * *".</code></pre>

Name



Crontab - files used to schedule the execution of programs



Description



A crontab file contains instructions for the cron daemon in ...

What is Crontab? - TCMHACK

What is Crontab?

Moving files and directories is one of the most basic tasks you often need to perform on a Linux system.



In this tutorial, we will explain how to use the&nbsp;<code>mv</code>&nbsp;command to move files and directories.



<h2 id="how-to-use-the-mv-command">How to Use the mv Command</h2>



The&nbsp;<code>mv</code>&nbsp;command (short from move) is used to rename and move and files and directories from one location to another. The syntax for the&nbsp;<code>mv</code>&nbsp;command is as follows:



<pre class="wp-block-code"><code>mv [OPTIONS] source destination</code></pre>



The&nbsp;<code>source</code>&nbsp;can be one or more files or directories and&nbsp;<code>destination</code>&nbsp;can be a single file or directory.



<ul><li>If you specify multiple files or directories as a <code>source</code>, the <code>destination</code> must be a directory. In this case, the <code>source</code> files are moved to the target directory.</li><li>If you specify a single file as <code>source</code>, and the <code>destination</code> target is an existing directory then the file is moved to the specified directory.</li><li>If you specify a single file as <code>source</code>, and a single file as <code>destination</code> target then you’re renaming the file.</li><li>If the <code>source</code> is a directory and <code>destination</code> doesn’t, exist <code>source</code> will be renamed to <code>destination</code>, otherwise it be moved inside the <code>destination</code> directory.</li></ul>



To move a file or directory you need to have write permissions on both <code>source</code> and <code>destination</code>. Otherwise, you will receive a permission denied error.



For example, to move the file&nbsp;<code>file1</code>&nbsp;from the current working directory to the&nbsp;<code>/tmp</code>&nbsp;directory you would run:



<pre class="wp-block-code"><code>mv file1 /tmp</code></pre>



To rename a file specify the destination file name:



<pre class="wp-block-code"><code>mv file1 file2</code></pre>



The command for moving directories is the same as when moving files. In the following example if the&nbsp;<code>dir2</code>&nbsp;directory exists the command will move&nbsp;<code>dir1</code>inside&nbsp;<code>dir2</code>. If&nbsp;<code>dir2</code>&nbsp;doesn’t exist,&nbsp;<code>dir1</code>&nbsp;will be renamed to&nbsp;<code>dir2</code>:



<pre class="wp-block-code"><code>mv dir1 dir2</code></pre>



<h2 id="moving-multiple-files-and-directories">Moving Multiple Files and Directories</h2>



To move multiple files and directories, specify the files you want to move as the source. For example to move the files&nbsp;<code>file1</code>&nbsp;and&nbsp;<code>file2</code>&nbsp;to the&nbsp;<code>dir1</code>&nbsp;directory you would type:



<pre class="wp-block-code"><code>mv file1 file2 dir1</code></pre>



The&nbsp;<code>mv</code>&nbsp;command also allows you to use pattern matching. For example, to copy all pdf files from the current directory to the&nbsp;<code>~/Documents</code>&nbsp;directory you would use:



<pre class="wp-block-code"><code>mv *.pdf ~/Documents</code></pre>



<h2 id="mv-command-options">mv Command Options</h2>



The <code>mv</code> command accepts options that affect default command behavior. In some Linux distributions <code>mv</code> may be an alias to the <code>mv</code> command with a custom set of options. For example in CentOS <code>mv</code> is an alias to <code>mv -i</code>. You can find whether <code>mv</code> is an alias using the <code>type</code> command:



<pre class="wp-block-code"><code>type mv</code></pre>



If&nbsp;<code>mv</code>&nbsp;is alias the output will look something like this:



<pre class="wp-block-code"><code>mv is aliased to `mv -i'</code></pre>



If you specify conflicting options, the option specified last takes precendence.



<h3 id="prompt-before-overwriting">Prompt before overwriting</h3>



By default if the destination file exists it will be overwritten. To prompt for confirmation use the&nbsp;<code>-i</code>&nbsp;option:



<pre class="wp-block-code"><code>mv -i file1 /tmp</code></pre>



<pre class="wp-block-code"><code>mv: overwrite '/tmp/file1'?</code></pre>



To overwrite the file type the character&nbsp;<code>y</code>&nbsp;or&nbsp;<code>Y</code>.



<h3 id="force-overwriting">Force overwriting</h3>



If you try to overwrite a read only file the&nbsp;<code>mv</code>&nbsp;command will prompt you whether you want to overwrite the file:



<pre class="wp-block-code"><code>mv -i file1 /tmp</code></pre>



<pre class="wp-block-code"><code>mv: replace '/tmp/file1', overriding mode 0400 (r--------)? </code></pre>



To avoid being prompted use the&nbsp;<code>-f</code>&nbsp;options:



<pre class="wp-block-code"><code>mv -f file1 /tmp</code></pre>



This option is especially useful when you need to overwrite multiple reed only file.



<h3 id="do-not-overwrite-existing-files">Do not overwrite existing files</h3>



The&nbsp;<code>-n</code>&nbsp;option tells&nbsp;<code>mv</code>&nbsp;never to overwrite any existing file:



<pre class="wp-block-code"><code>mv -f file1 /tmp</code></pre>



If a&nbsp;<code>file1</code>&nbsp;exists the command above will do nothing, otherwise it will copy the file to the&nbsp;<code>/tmp</code>&nbsp;directory.



<h3 id="backing-up-files">Backing up files</h3>



If the destination file exists you can create a backup of it using the&nbsp;<code>-b</code>&nbsp;option:



<pre class="wp-block-code"><code>mv -b file1 /tmp</code></pre>



The backup file will have the same name as the original file with a tilde (<code>~</code>) appended to it.



Use the ls command to verify that the backup was created:



<pre class="wp-block-code"><code>ls /tmp/file1*</code></pre>



<pre class="wp-block-code"><code>/tmp/file1 /tmp/file1~</code></pre>



<h3 id="verbose-output">Verbose output</h3>



Another option that can be useful is&nbsp;<code>-v</code>. When using this option the command will print the name of each moved file:



<pre class="wp-block-code"><code>mv -i file1 /tmp</code></pre>



<pre class="wp-block-code"><code>renamed 'file1' -> '/tmp/file1'</code></pre>



<h2 id="conclusion">Conclusion</h2>



By now you should have a good understanding of how to use the&nbsp;<code>mv</code>&nbsp;command to move files and directories. New Linux users who are intimidated by the command line can use the GUI file manager to move their files.



For more information about the <code>mv</code> command check the <a href="https://ss64.com/bash/mv.html" target="_blank" rel="noreferrer noopener" aria-label=" (opens in a new tab)">man page</a>.



If you have any question or feedback, feel free to leave a comment.

Moving files and directories is one of the most basic tasks you often need to perform on a Linux system.



In this tutorial, we will explain how...

Linux Shutdown Command

Basic & Useful Linux Commands

What is Crontab?

How to Move Files and Directories in Linux with the mv Command