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  <p>Post about modifying crontab using ssh</p>
</blockquote>



<h2 id="environment-and-prerequisite">Environment and Prerequisite</h2>

<ul>
  <li>Linux</li>
  <li>SSH(OpenSSH)</li>
  <li>crontab</li>
</ul>



<h2 id="how">How</h2>

<h3 id="crontab">crontab</h3>

<div><pre><code>crontab [-u user] file
crontab [-u user] { -l | -r [-f] |	-e }
</code></pre></div>

<ul>
  <li>Give standard input(stdin) or filename after crontab command overwrite crontab content to that standard input(stdin) or file.</li>
  <li><code>crontab -e</code> cannot be used in ssh command so use above method.</li>
  <li><a href="https://www.freebsd.org/cgi/man.cgi?query=crontab&amp;apropos=0&amp;sektion=1&amp;manpath=FreeBSD+12.2-RELEASE+and+Ports&amp;arch=default&amp;format=html">Document</a> says “The first form of this command is used to install a new crontab from some named file	or standard input if the pseudo-filename ‘-‘ is	given”.</li>
</ul>



<h3 id="example">Example</h3>

<h4 id="scenario">Scenario</h4>

<ul>
  <li>Modify server’s crontab from current computer</li>
</ul>

<h4 id="example-1">Example</h4>

<ul>
  <li>Check crontab content in server</li>
</ul>

<div><pre><code><span># Check remote crontab</span>
ssh twpower@157.230.234.230 <span>"crontab -l"</span>
</code></pre></div>

<div><pre><code>0 10 17 <span>*</span> <span>*</span> /home/twpower/simple-script.sh
40 7 <span>*</span> <span>*</span> 1 python /home/twpower/run.py
</code></pre></div>

<ul>
  <li>Modify crontab content and apply it after copy crontab content to <code>/tmp</code>.</li>
</ul>

<div><pre><code><span># Copy current crontab content to temporary file</span>
ssh twpower@157.230.234.230 <span>"crontab -l &gt; /tmp/tmp-crontab-content"</span>

<span># Add crontab content to temporary file</span>
<span># Not only addition but also deletion and modification are possible</span>
<span># Many variations are possible like using sed, tee or cat</span>
ssh twpower@157.230.234.230 <span>"echo '* * * * 1 python /home/twpower/run.py' &gt;&gt; /tmp/tmp-crontab-content"</span>

<span># Apply new crontab using temporary file</span>
ssh twpower@157.230.234.230 <span>"crontab /tmp/tmp-crontab-content"</span>

<span># Remove temporary file</span>
ssh twpower@157.230.234.230 <span>"rm -rf /tmp/tmp-crontab-content"</span>
</code></pre></div>

<ul>
  <li>Check result</li>
</ul>

<div><pre><code><span># Check remote crontab</span>
ssh twpower@157.230.234.230 <span>"crontab -l"</span>
</code></pre></div>

<div><pre><code>0 10 17 <span>*</span> <span>*</span> /home/twpower/simple-script.sh
40 7 <span>*</span> <span>*</span> 1 python /home/twpower/run.py
<span>*</span> <span>*</span> <span>*</span> <span>*</span> 1 python /home/twpower/run.py
</code></pre></div>

<h4 id="script">Script</h4>

<ul>
  <li>It can be made to script like below.</li>
</ul>

<div><pre><code><span>#!/bin/bash</span>

<span># Copy current crontab content to temporary file</span>
ssh twpower@157.230.234.230 <span>"crontab -l &gt; /tmp/tmp-crontab-content"</span>

<span># Add crontab content to temporary file</span>
<span># Not only addition but also deletion and modification are possible</span>
<span># Many variations are possible like using sed, tee or cat</span>
ssh twpower@157.230.234.230 <span>"echo '* * * * 1 python /home/twpower/run.py' &gt;&gt; /tmp/tmp-crontab-content"</span>

<span># Apply new crontab using temporary file</span>
ssh twpower@157.230.234.230 <span>"crontab /tmp/tmp-crontab-content"</span>

<span># Remove temporary file</span>
ssh twpower@157.230.234.230 <span>"rm -rf /tmp/tmp-crontab-content"</span>
</code></pre></div>



<h2 id="reference">Reference</h2>

<ul>
  <li><a href="https://www.freebsd.org/cgi/man.cgi?query=crontab&amp;apropos=0&amp;sektion=1&amp;manpath=FreeBSD+12.2-RELEASE+and+Ports&amp;arch=default&amp;format=html">https://www.freebsd.org/cgi/man.cgi?query=crontab&amp;apropos=0&amp;sektion=1&amp;manpath=FreeBSD+12.2-RELEASE+and+Ports&amp;arch=default&amp;format=html</a></li>
</ul>

      
        
        
        </div>
    
    
    

  </article>
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TWpower’s Tech Blog

Post about modifying crontab using ssh
Environment and Prerequisite
Linux
SSH(OpenSSH)
crontab
How
crontab
crontab [-u user] file
crontab [-u user] { -l | -r [-f] |	-e }
Give standard input(stdin) or filename after crontab command overwrite crontab content to that standard input(stdin) or file.
crontab -e cannot be used in ssh command so use above method.
Document says “The first form of this command is used to install a new crontab from some named file	or standard input if the pseudo-filename ‘-‘ is	given”.
Example
Scenario
Modify server’s crontab from current computer
Example
Check crontab content in server
# Check remote crontab
ssh twpower@157.230.234.230 "crontab -l"
0 10 17 * * /home/twpower/simple-script.sh
40 7 * * 1 python /home/twpower/run.py
Modify crontab content and apply it after copy crontab content to /tmp.
# Copy current crontab content to temporary file
ssh twpower@157.230.234.230 "crontab -l > /tmp/tmp-crontab-content"
# Add crontab content to temporary file
# Not only addition but also deletion and modification are possible
# Many variations are possible like using sed, tee or cat
ssh twpower@157.230.234.230 "echo '* * * * 1 python /home/twpower/run.py' >> /tmp/tmp-crontab-content"
# Apply new crontab using temporary file
ssh twpower@157.230.234.230 "crontab /tmp/tmp-crontab-content"
# Remove temporary file
ssh twpower@157.230.234.230 "rm -rf /tmp/tmp-crontab-content"
Check result
# Check remote crontab
ssh twpower@157.230.234.230 "crontab -l"
0 10 17 * * /home/twpower/simple-script.sh
40 7 * * 1 python /home/twpower/run.py
* * * * 1 python /home/twpower/run.py
Script
It can be made to script like below.
#!/bin/bash
# Copy current crontab content to temporary file
ssh twpower@157.230.234.230 "crontab -l > /tmp/tmp-crontab-content"
# Add crontab content to temporary file
# Not only addition but also deletion and modification are possible
# Many variations are possible like using sed, tee or cat
ssh twpower@157.230.234.230 "echo '* * * * 1 python /home/twpower/run.py' >> /tmp/tmp-crontab-content"
# Apply new crontab using temporary file
ssh twpower@157.230.234.230 "crontab /tmp/tmp-crontab-content"
# Remove temporary file
ssh twpower@157.230.234.230 "rm -rf /tmp/tmp-crontab-content"
Reference
https://www.freebsd.org/cgi/man.cgi?query=crontab&apropos=0&sektion=1&manpath=FreeBSD+12.2-RELEASE+and+Ports&arch=default&format=html

[Linux](EN) Modify crontab using ssh

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