I was working on a CentOS 7 server the other day that had a LAMP stack installed. It was used to host only a single instance of WordPress. Upgrading themes and plugins from the admin interface worked fine, but curiously, WordPress core upgrades did not. Instead, WordPress was asking for FTP details every time, which also … Read more
CentOS 6 comes with Python 2.6 installed, and CentOS 7 comes with Python 2.7. But right now, Python 3.5 is all the rage, so I thought I’d install it alongside Python 2.x on the same machine.
Here’s how I did it.
I’m using a CentOS 6 32 bit system here, but I’ve tried the same on a CentOS 7 64 bit rig. You need to be root or have superuser privileges to do this successfully.
I’ve recently come across a tarsal files that used xz compression (namely the Python source code). This means that my usual way of extracting a tarsal via the command line using the following command did not work: tar -zxvf Python* gzip: stdin: not in gzip format tar: Child returned status 1 tar: Error is not … Read more
In CentOS 7 we can use the systemctl command to select which mode the OS boots into. If you have a GUI like Gnome or KDE installed, it’s easy to boot directly into your preferred environment. To find out what mode CentOS is currently using, use this: systemctl get-default This will give you one of … Read more
I’ve come across an odd problem today on a server that’s been working fine for all kinds of FTP traffic for many years. Turns out that today, FileZilla started complaining about explicit TLS connections (when available) and gave the following error message: 425 MLSD unable to build data connection: operation not permitted Clients could still … Read more
There are two funky commands that can help us see who’s currently logged in, and what operations were performed last. Those two commands are who and last. Let me show you how to use them. The who command Type who at the command prompt and you’ll see a list of currently logged-in users: who versluis … Read more
Today I was introduced to something called the CBL, or the Composite Blocking List. This is one of several Spamhaus projects that’s there to make sure IP’s are blacklisted when they’re sending spam.
You can check if your IP’s are OK at http://www.spamhaus.org/lookup/
The CBL is a separate website in which you can also lookup IPs. Spamhaus will tell you if that’s the case and direct you to the CBL here: http://www.abuseat.org/lookup.cgi
Even though my IP was otherwise fine, it was listed in the CBL, and Yahoo kindly made me aware of this as part of an error message I’ve received when trying to send an email. If ever there is an email problem in CentOS, the first place to look is /var/log/maillog. Here’s Yahoo’s very helpful explanation: https://help.yahoo.com/kb/postmaster/SLN5070.html
Turns out that the hostname was not setup yet, so the box would respond as localhost.localdomain. That’s a big fat no-no as far as the CBL people are concerned. Here’s CBL’s explanation:
This IP address is HELO’ing as “localhost.localdomain” which violates the relevant standards (specifically: RFC5321).
The CBL does not list for RFC violations per-se. This _particular_ behaviour, however, correlates strongly to spambot infections. In other words, out of thousands upon thousands of IP addresses HELO’ing this way, all but a handful are infected and spewing junk. Even if it isn’t an infection, it’s a misconfiguration that should be fixed, because many spam filtering mechanisms operate with the same rules, and it’s best to fix it regardless of whether the CBL notices it or not.
CentOS 7 has a nice command called hostnamectl. With it we can display the current hostname, and set any of the three types of hostname: static hostname (something like example.com) transient hostname (anything you like, assigned when using DHCP) pretty hostname (something like Jay’s MacBook Pro) By default, a CentOS installation comes back with localhost.localdomain … Read more
