Why does my debian server freeze?

I installed Debian 9 ("Stretch") in a virtual machine hosted on ESXi 6.5 The OS is up-to-date and nothing else has been installed but VMware tools.

Sometimes when I execute a command, the server will freeze and nothing can be done besides resetting the VM (the SSH server becomes unresponsive, all terminals are freezed, it doesn't show a KP or anything else)

I can reproduce the problem very easily: I just have to execute wget a couple of times and the OS will hang.

At first, I thought it could be a RAM problem. I used memtest86+ on the host and no problem was found. I also tried the debian package "memtester" which runs very well in the VM and doesn't make the OS freeze whatsoever.

/var/log/messages shows nothing special, but there's one line I don't understand:

Jul  3 13:05:57 myhost kernel: [   58.966715] TCP: ens192: Driver has suspect GRO implementation, TCP performance may be compromised.

What could be the problem and how can I debug the whole thing?

Config: 1 CPU / 4 cores - 32GB Ram - 64GB HDD

Solution 1:

I had this exact scenario going on. Created a Debian 9 VM under ESXi 6.5 and it would freeze when running a few commands. Also, when I closed an SSH session, it would completely freeze and my only option was to reboot.

I fixed it by changing the network adapter type for this host from the default "VMXNET 3" to "E1000e".

Solution 2:

If it is a VM, and you can change some parameters, try to set up another type of network adapter, as that looks network related.

Also, check also the dmesg output from time to time, even if it is working ok, as it may show other problems.