After being forced to work with Windows for a while I finally was able to switch back to Linux. And one of the first things I needed for work was MS Teams. So I updated the already installed version and when I first had to do a screen share I had a flashback, why I switched to use Teams in a VM, rather than the native Linux version: a grey overlay.
It’s nice to have the red frame, so that I know which screen I am sharing, but the grey overlay makes things very hard to read. Especially when you share a dark themed window. But see for yourself. This is what I got:
It has been a while since my last blog post, but there was no real foo happening to me during that time. But this issue really gave me some heartburn.
Let’s start with the general setup. We have a Linux VM in an OpenVZ environment. The hoster is Strato in Germany, but I don’t think that really matters. There are some known issues with the TUN device not being accessible within the VM, but Strato did their homework and I could see the module:
# lsmod | grep tun
tun 4242 -2
vznetstat 4242 -2 tun,ip_vznetstat,ip6_vznetstat
I chose a nice Friday evening and a good Scotch to upgrade an older Ubuntu LTS to the latest and greatest. And all went well, until I wanted to connect one of the clients via VPN. All I saw was this nasty little line in the log files of the server
... VERIFY ERROR: depth=0, error=CRL has expired: ...
Sending email in Linux is pretty straight forward, once an email server is set up. Just use mutt or mail and all is good. But sometimes you actually want to test if SMTP is working correctly. And not only on your box, but on a remote box. That is of course easy using a MUA like Thunderbird or Sylpheed, but that is not always feasible on a remote server in a remote network.
After moving a server to a new machine with Ubuntu 16.10 I received some strange Postfix SMTP errors. Which turned out to be a connection issue to the MySQL server:
postfix/cleanup: warning: connect to mysql server 127.0.0.1: Too many connections
Oops, did I forgot to up max_connections during the migration:
It was that time of the year, when I had to renew some SSL certificates. Renewing and updating them in the server is a nice and easy process. But checking, whether the server is delivering the correct certificate and, that I updated and popluated the intermediate certificates correctly, is a different story.
While debugging my check disk problem after the 15.10 upgrade, I saw that I forgot to enable external commands. That is handy, when you want to re-schedule a check to see, if your changes took effect. Again, something that is easily activated. So if you see something like this, then you might want to make some changes:
Error: Could not stat() command file ‘/var/lib/nagios3/rw/nagios.cmd’!
Cleaning up old kernel images on a Ubuntu machine is a quite annoying task. If you forget it and you have a separate /boot partition, then you will sooner or later run out of disk space. And then of course all your updates will fail.
Doing the clean up manually is, as mentioned, more than annoying and very tedious. But other smart people have spent some time and created a nice little one-liner that will get rid of old kernel versions. This command line will of course make sure that the currently running kernel is not removed. So it is very important to reboot after a kernel upgrade before you run this script!
And without further ado I present….
dpkg -l 'linux-*' | sed '/^ii/!d;/'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d;s/^[^ ]* [^ ]* \([^ ]*\).*/\1/;/[0-9]/!d' | xargs apt-get -y purge
Not a big deal but a sudo snuck into the xargs call. It is now removed and shouldn’t cause any trouble anymore.
The last Chrome update and one of the last Thunderbird updates caused some strange crashes of either on of them on my Ubuntu 13.10. All is fine, it runs great and all of a sudden *boom*, browser window gone, or email client gone.
Luckily .xsession-errors exists and there I could find some entries like this:
[3827:4038:0518/230904:ERROR:shared_memory_posix.cc(226)] Creating shared memory in /dev/shm/.com.google.Chrome.12UDei failed: Too many open files
Not good. But there is help. For MyEclipse I had the same issue in the past. But it didn’t seem necessary anymore since 13.10. But I also haven’t used it in a while. Anywhoo, here is what has to be done. And before I forget it, all these changes have to be done as root.
First check the setting for file-max with the following command
In my case this value seems fine, as it is well beyond the 200,000 that they recommend.
peter@majestix:~$ cat /proc/sys/fs/file-max
If that is below 200,000 you can set by adding the following line to /etc/sysctl.conf
The next is the ulimit setting for open files. You can check it with the following command
This one was set to 1024 in my case and that can be a little bit low. At MyEclipse they recommend setting it to 65535 and that’s what I did. Just add the following lines to /etc/security/limits.conf
* hard nofile 65535
* soft nofile 65535
Afterwards restart your machine and all should be fine. If you only have to change the sysctl.conf setting then you can activate that change with the following command
service procps start