When preparing for the RHCSA and RHCE exams, I found several useful commands I was not really aware of. In this blog post I’ll share them with you.
findmnt command is part of the essential package util-linux and hence is available on pretty much all Linux systems. It can print all mounted filesystems in the tree-like format. I found the output of
findmnt command more readable than the output provided by the more popular
mount command. This is an example of how the filesystem mounts on a Ceph node look like:
ss (soscket statistics) command is a replacement for the good old
netstat command. It comes in the iproute package which is an essential part of all modern Linux distributions. I found
ss command available on systems where the
netstat command was missing. Here is a sample output of the
ss command running on my Linux desktop:
I’m switching from using the
netstat command to
ss. What about you?
After years of using the
ifconfig utility, it took me some effort to move to its modern replacement - the
ip command. Recently, I discovered two useful features of the
To obtain a detailed information about the packets transferred by individual network interfaces, use the
-s (statistics) parameter. For example:
To figure out which network interface would be used to send a packet to the specified IP address:
When sending a packet to the target destination
192.168.0.1, the kernel will route the packet via the
enp0s31f6 interface. The IP
10.5.0.1 is my default route.
On modern machines the output of
cat /proc/cpuinfo can be really long. To find out what CPU configuration a machine comes with I prefer to use the
lscpu command. This is an example output of the
lscpu command running on an OpenStack compute node:
In the above output, the interesting lines are the
Core(s) per socket,
Thread(s) per core and
CPU(s). In our case, we’re looking at a machine with 2 physical CPUs (Sockets), each of them having 8 physical cores (Cores per socket). Each of the physical cores has 2 processing threads (Threads per core) aka logical CPUs due to the Hyper-Threading technology. In total, there are 32 logical CPUs available to the Linux scheduler to schedule a task on.
The last command in our overview is the
lspci command. If you ever wondered which kernel driver is controlling your hardware device, you can find out with: