When you install or update packages on your system, then changes may occur that were not expected. A recent security update on a server and left Nagios in a failed state, but what exactly happend and can it be traced back as yum-cron installs all required security updates? Luckily YUM keeps a history database of all actions and with yum history can you list all transactions.
As transaction 15 was the latest and only transaction before the defect occurred it is the one to look into. With yum history info the details of the transaction can be shown. It show when and who triggered the transaction, but also with which version of RPM, YUM and which plugins for YUM were used. Most important it also shows which package were updated with versions used and from which repository. This narrows the search down to the packages shown as updated and see what they changed on the system.
$ sudo yum history info 15
Loaded plugins: fastestmirror
Transaction ID : 15
Begin time : Sat Feb 2 07:30:58 2019
Begin rpmdb : 450:5f24b4b6a7aaef9f42874d6c8643385133020181
End time : 07:31:04 2019 (6 seconds)
End rpmdb : 450:246b0b638aa8b6b851529eb1b040714b7149d0e9
User : root <root>
Return-Code : Success
Transaction performed with:
Installed rpm-4.11.3-32.el7.x86_64 @anaconda
Installed yum-3.4.3-158.el7.centos.noarch @anaconda
Installed yum-plugin-fastestmirror-1.1.31-46.el7_5.noarch @updates
Updated nagios-4.3.4-5.el7.x86_64 @epel
Update 4.4.3-1.el7.x86_64 @epel
Updated nagios-common-4.3.4-5.el7.x86_64 @epel
Update 4.4.3-1.el7.x86_64 @epel
Red Hat Linux 8 will be using dnf instead of yum like Fedora 18 and later, but you don’t have to relearning anything as you can use dnf in the same way as yum and with the same parameters for now.
HTTPS may become the standard quickly, but HTTP is still the base and understanding how to verify an HTTP server without a web browser can be very useful. A lot of situations simply don’t allow you to install a web browser or gives only a blank page.
As HTTP is a plain-text protocol you can simulate a connection with telnet on the command line. So let connect to fresh Linux machine with Apache running and see what happens. After connecting you type in “GET /index.html HTTP/1.1” to tell webserver which file you want to get and in this case the file in /index.html. The second line tells the webserver for which website you make the request which is 192.168.121.7.xip.io in the example. And finally you give an additional enter to tell your request is complete and can be processed after which you get the response.
$ telnet 192.168.121.7.xip.io 80
Connected to 192.168.121.7.
Escape character is '^]'.
GET /index.html HTTP/1.1
HTTP/1.1 404 Not Found
Date: Sun, 06 Jan 2019 01:27:00 GMT
Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips PHP/7.3.0
Content-Type: text/html; charset=iso-8859-1
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<title>404 Not Found</title>
<p>The requested URL /index.html was not found on this server.</p>
Connection closed by foreign host.
The response in the example tells that the file index.html doesn’t exist on the webserver, which is correct for this example. It also give additional metadata about the server and the form the content is served which can be handy to see if the mimetype matches or the response size is correct.
Last month PHP 7.3.0 was released and with that a lot of functions or aliases were deprecated that may lead to issues down the road. While Xdebug still needs to be released for PHP 7.3 an automated test with GitLab isn’t possible yet as the build phase of Xdebug fails. Luckily I’m using PHP Code Sniffer and extending phpcs.xml.dist with the lines below make the build already fail if any of the forbidden functions are being used in the code.
exFAT has been chosen by the SD Card Association as the standard file system for SDXC cards with 32 GiB or more of storage. Sadly the Fedora Project has chosen not to bundle support for exFAT due to patent issues. A free implementation of exFAT has been made and is available via RPMFusion Free for RPM based systems.
Solid state drives sound ideal as they have no spinning parts and are very quiet, but they have a limited lifespan as you can’t write a memory cell only an X amount of times. But how to check your SSD on Linux to see if it is still in good shape? S.M.A.R.T. has become the standard for disk health years ago and can be queried by smartctl. So if we query for the health status and show all available attributes we get a good overview.
The most interesting attributes are 202 on how much lifetime is left, but also 5, 180 and 9 that show your the number of replaced storage cells and how many hours the disk has been running. If attribute 5 and 180 are changing it is most definitely time to replace this solid state drive as memory cells have been worn out.