Locking and Unlocking a User in Ubuntu

Posted on February 19, 2016 by curiouscat

To lock a user in Ubuntu sudo usermod –expiredate 1 [username] Substitute the user’s username where username is shown below.

[code]sudo usermod –expiredate 1 username[/code]

This also can be shortened to

[code]sudo usermod -e 1 username[/code]

To unlock a user

[code]sudo usermod -e -1 username[/code]

This will disable the user both from accessing via password and from accessing via a private key.

You can also expire a user at a future date using

[code]sudo usermod -e YYYY-MM-DD username[/code]

To expire a password and force a user to enter a new password

[code]sudo passwd -e YYYY-MM-DD username[/code]

How to Manually Run Cron Tasks

Posted on September 27, 2015 by curiouscat

To manually run cron tasks you can use the run-parts command in Linux.

So to run your cron-weekly, for example, to test that a fix you just made runs without error (this is what I just did, in fact)

run-parts /etc/cron-weekly

run-parts will run all the executables in a directory (you must point at the directory). So if you have several files in cron-weekly to run, you can’t just point to one of the files.

You may run into environmental differences running the script as a different user than the cron test runs at, so you can run as that user if needed. You need to be aware this is a quick and simple way of testing part of the process but it doesn’t do a perfect job of testing if it works as a cron task. But it will let you catch some failures quickly and fix them in time for the actual cron task to run. So do check that the everything works after the real cron job runs.

This is just the kind of thing I said I would put in this blog. Simple stuff but things I forget – so I put it here to remember and maybe help out others, like me, that need really basic tips.

If you have a cron task item (or have setup the whole task this way) that is just a script and you just want to test that 1 item you may run the script directly. For example (for a Linux shell script):

sh /etc/cron.weekly/your_crontask_script.sh

Compare WordPress Files on Server to Proper WordPress Version

Posted on November 18, 2014 by curiouscat

Sadly one of the hassles in managing your own WordPress blog is dealing with people that use your blog to serve spam content. These hacks can insert spam links into your pages and posts or create spam directories that are completely their own content on your domain.

There are many issues to deal with in re-establishing control of your server; but that isn’t the scope of this post.

This is just a tips if you are troubleshooting to try and determine what is going on. Often your server has been hacked to allow uploaded php pages to be added or for WordPress php files to be edited.

One way to track down if the files have been changed or new ones added is to compare the WordPress files on your server to the current files for a fresh WordPress install. This assumes your blog is using the current version, which hopefully it is because on the big improvement WordPress made is to make those updates automatic. That greatly reduces the chance to have WordPress be the vector to infecting your server. If you were using a older version then just compare to the field for that version from the WordPress server.

If you don’t have a current backup I would make a backup before I tried this. Obviously, don’t make any deletions or changes to your server unless you understand what you are doing. You can create big problems for yourself.

You can use the diff command to view the difference between WordPress on your sever and the fresh install from WordPress. I install the new WordPress in a new directory outside public_html. At the cli on a Ubuntu/Linux server:

[code]sudo wget http://wordpress.org/wordpress-4.0.zip
unzip wordpress-4.0.zip
diff -rq wordpress ../public_html/[/code]

wordpress-4.0.zip – replace with whatever the version is you are using.
../public_html/blog/ – replace with the path to your blog

Continue reading →

VPS, Cloud and Server Colocation Options

Posted on October 23, 2014 by curiouscat

Finding the right place to host your content is important. Thankfully their are several excellent providers. For virtual private servers (one server shared with multiple virtual servers) Linode and DigitalOcean. And there are lots of good choices but those two are widely appreciated for excellent service at a good price.

AWS ec2 (the Amazon elastic cloud) is not great for minimal hosting in my opinion – it adds extra complexity and is likely more expensive. But it is a great solution when you have the resources to manage it and you have significantly variable demand. Because of the ability to add capacity on the fly as you need it you can maintain a low baseline and add capacity only as needed and drop that extra capacity as soon as it isn’t needed.

Rackspace is another good option for hosting. Rackspace and AWS are often used for very large applications and sites but Linode and Digital Ocean also can serve those needs and provide similar options to add capacity on the fly.

All of these options require you to manage your server (which may well be a virtual server – that is just a portion of a actual physical server that you control).

Rackspace also offers co-location where your physical server is put in their network operation center with electricity; cooling; network and internet connections; and physical security managed by them and the server managed by you.

As colocation has evolved what is included and to what level things like physical security and redundancy are dealt with have evolved. It has become quite complex to understand all the options for those organizations that need more than a simple virtual private server. As often happens when their is a business need, people offer solutions. And there are companies that specialize in helping you find the best colocation options for your needs.

Today the cloud options have led many organizations to eliminate (or greatly reduce) there own network operations centers and colocation needs. But cloud options are not always the right choice. And for some needs cloud options are not appropriate yet (mainly due to security or legal issues stemming from security concerns).

Managing your own servers with a colocation arrangement can be significantly cheaper than cloud hosting options (especially if you don’t need to massively increase capacity to deal with short term bursts of demand). Of course, technology continues to change so quickly it is hard to predict what the future will bring.

Service quality is absolutely critical for colocation. While saving money is important, the reason colocation was selected (over virtual private servers or the cloud) is normally how critical the function was. Using experts to help sort through the options and assure the quality of service of provides is wise.

Turn It Off and On Again

Posted on May 8, 2014 by curiouscat

I had a WordPress blog lose the database connection. As I tried to troubleshoot it I rapidly got to the point of thinking that maybe just rebooting the server would fix things – since no changes had been made that should cause the database connection to be lost. But also I figured I couldn’t be so lucky that such a simple thing would work.

I tried to log into the database using the cli and it was failing. MySQL was still running – according to top. I have automated security updates setup for the VPS server running Ubuntu. My thought now is those updates somehow messed things up to the extent the server database connections somehow wasn’t working. I sure hoped that was the case.

I rebooted and hoped.

After a bit I was able to see that it was working.

When I went to reboot I noticed I hadn’t rebooted in a long time. My guess is I might have the automated security updates setup wrong on this server (maybe it is installing more than just the security updates), I’ll check. I have not had this problem before with other servers, obviously breaking a database in this way would cause lots of problems on production machines so I tend to think it is more likely I messed something up than this is a likely outcome when using automated security updates (but such things are possible which is why I think places with full time system admins and important servers rely on manual updates with professionals watching everything to be sure nothing obvious breaks).

My feeling is the longer you go with not rebooting the server the more likely some issues are to crop up (but also every reboot is more like to result in some broken thing, right then, than doing nothing so it is a tradeoff). And I could be wrong in that feeling, it is just what I guess without much evidence to support my guess.

Anyway I was very happy turning it off and on again worked. Honestly I went ahead and updated the server before I rebooted, but my guess is just turning it off and on again would have worked.

Upgrading VPS Web Server from Ubuntu 10.04 to 12.04

Posted on October 15, 2012 by curiouscat

I am not a “real” system administrator but I manager sever VPS servers for my own web sites. This is what I did to update from Ubunutu LTS 10.04 to Ubunutu VPS 12.04.

I already have all the code and databases backed up, off the server, regularly. I backed up various things to another machine: sites-available files, cron directories, .bashrc, .profile, keys.
I tried running the preferred upgrade command
[bash]do-release-upgrade[/bash]

But got the message

-bash: do-release-upgrade: command not found

Then I ran

[bash]sudo apt-get install update-manager-core[/bash]

Then I was able to run [bash]sudo do-release-upgrade[/bash]
Which resulted in this somewhat scary message

This session appears to be running under ssh. It is not recommended to perform a upgrade over ssh currently because in case of failure it is harder to recover.

If you continue, an additional ssh daemon will be started at port ‘9004’.
Do you want to continue?

I look around on the web for advice. What’s the risk of upgrading over SSH? seems a good recap. I then continued. I then got this message

To make recovery in case of failure easier, an additional sshd will be started on port ‘1022’. If anything goes wrong with the running ssh you can still connect to the additional one.
If you run a firewall, you may need to temporarily open this port. As this is potentially dangerous it’s not done automatically. You can open the port with e.g.:
‘iptables -I INPUT -p tcp –dport 1022 -j ACCEPT’
12 minutes after the upgrade started, the download was complete and I got a message to decide if I wanted to manually approve every restart required or just automatically approve them all. I chose the option to have all restart automatically.
Then lots of files were installed and I was asked about various files; where I (or some script) had changed (or deleted) the default file and now the upgrade wanted to replace the existing file. I had to guess what to do in those cases. They let you look at the diff between your existing file and the proposed overwrite. I think I would like it if they default behavior was to create a backup of the file in that same directory (you choosing whether to set your file or the updated file as active).

The entire process took exactly 30 minutes, with the system restarting in Ubuntu 12.04.

Thankfully the upgrade seems to have gone without causing any problems. This is normally the case. But, even with a very small likelihood of encountering issues it is worrisome as those issues might pose some serious problems. Especially for someone with very limited system administration ability.

I am extremely thankful for all the programmers that created the code to make this process so straightforward and reliable.

[bash]lsb_release -a[/bash]

lets you see the current Ubunutu version you are running.

When I updated a server that had Ruby on Rails applications everything almost worked fine. Passenger was unable to load the application talking about

libmysqlclient_r.so.16: cannot open shared object file: No such file or directory – /usr/local/rvm/gems/ruby-1.9.2-p290/gems/mysql2-0.3.11/lib/mysql2/mysql2.so

I was able to find the solution to that issue was to uninstall the mysql2 gem and then run bundle update: which worked great. The uninstall would work for me unless I was actually root (sudo didn’t work), so I used su to login as root and then

[bash]gem uninstall mysql2[/bash]

Then I went back to being my other user ran bundle update

[bash]bundle update rake[/bash]

Then everything was working fine.

Set the Web Server to Use the Domain Without www

Posted on April 26, 2012 by curiouscat

The main reason to bother with this is to help search rankings. Sub-domains (for example, www.curiouscat.com and curiouscat.com) are treated as separate websites even if you have entirely the same content displayed for both. If 20% of the links to your site use the www and 80% don’t then your sites ranking by search engines is less than it would be if it was just treated as one site.

You can set the domain to use in Google webmaster tools. But that doesn’t do anything for all the other search engines. Also if you have both, some reports some will keep statistics separately for the non-www and www domain (Google Adsense does this, for example).

Using virtual hosts file (sites-enabled)

For Apache you can place the following code in your virtual hosts file (in the sites-available directory under Apache).

Replace curiouscat.com with your domain name.

[bash]<Directory /srv/www/curiouscat.com/public_html/>
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www.curiouscat.com$ [NC]
RewriteRule ^(.*)$ http://curiouscat.com/$1 [R=301,L]
</Directory>[/bash]

Then you need to capture the update and reload Apache.

Disable the site (in order to enable it with the updates)
[bash]sudo a2dissite curiouscat.com[/bash]
Enable the site
[bash]sudo a2ensite curiouscat.com[/bash]
Reload Apache (new way – Ubuntu 12.04)
[bash]sudo service apache2 reload[/bash]
Old way to reload Apache was > sudo /etc/init.d/apache2 reload

If when you try to reload you get this error message:

“Invalid command ‘RewriteEngine’, perhaps misspelled or defined by a module not included in the server configuration” then enable modrewrite on apache:

[bash]sudo a2enmod rewrite[/bash]

You should then be told to restart apache

[bash]sudo /etc/init.d/apache2 restart[/bash]

Using .htaccess

Or you can include the following in your .htaccess file

[bash] RewriteEngine On
RewriteCond %{HTTP_HOST} ^www.curiouscat.com$ [NC]
RewriteRule ^(.*)$ http://curiouscat.com/$1 [R=301,L][/bash]

If you wanted to force www to be used instead just flip the regular expression around:

[bash]<Directory /srv/www/curiouscat.com/public_html/>
RewriteEngine On
RewriteCond %{HTTP_HOST} ^curiouscat.com$ [NC]
RewriteRule ^(.*)$ http://www.curiouscat.com/$1 [R=301,L]
</Directory>[/bash]

Testing Email Using The Ubuntu CLI

Posted on April 17, 2012 by curiouscat

For a Virtual Private Server (VPS) or any other web or other server you should have alerts sent by email for various things. So for example if you automate security updates for an Ubuntu web server you want to be notified if there is some issue with the automatic update.

In order to check and be sure email is setup and working on the sever there is simple command line code to use:

[bash]mail -s Test[/bash]

you then get a prompt to enter

To: [enter the email and press return]

Cc: [press return]

then a blank where you can type in any text you want in the body of the message.

Then you send the message with by pressing CTRL-d

[bash]CTRL-d[/bash]

If you don’t receive the email then you can troubleshoot what is going wrong.

Keeping Your Hosted Ubuntu Web Server Software Up to Date

Posted on April 16, 2012 by curiouscat

To setup automatic security updates follow the instructions from Ubuntu.

To run security update manually

[bash]sudo unattended-upgrade[/bash]

A full update of all packages can be done using the follow, remember this may create some issues is one update makes something else you have no longer work properly. You should test to make sure things all work after the updates (for production systems obviously you should test things before [first updating the staging server to make sure the updates don’t cause any problems] and after the updates).

First update the local package index (to find what needs to be upgraded).

[bash]sudo apt-get update[/bash]

Then upgrade the software.

[bash]sudo apt-get upgrade[/bash]

Adding a Key to Your Server for SSH Login

Posted on April 5, 2012 by curiouscat

Using Ubuntu

An authentication key allows your server to authenticate the computer you are using has the right key and should be granted access. This lets you use the key instead of a username and password when using ssh.

If you don’t already have a key on your local machine (look for a file named id_rsa.pub in your user home directory under the .ssh folder

[bash]cd /.ssh[/bash]

will get you to the right directory) then you need to generate the key pair. On your desktop machine use:

[bash]ssh-keygen[/bash]

Next you copy the file to your server. scp ~/.ssh/id_dsa.pub [user]@[server]:.ssh/

[bash]scp ~/.ssh/id_dsa.pub username@servername:.ssh/[/bash]

Rename the file on the server to authorized_keys2
[bash]mv id_rsa.pub authorized_keys2[/bash]

The key is for to authenticate your computer. But on the ssh login Ubuntu will look in the user folder. So if you also had user2 access to the server and tried to ssh into the server you would not be authenticated because it would look in user2/.ssh for the authorized key file and not find it. You can put the same key in any user folder on your server to have that user also be automatically authenticated.

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