strace is a tool that inspect what an application is doing. You can strace application on launch or attach a running one to strace using its PID. It will show you all files and system call calls the process is using and calling.
This is a nice introduction on strace with examples.
Flash and SSD storage devices are faster than spinning disks because they have no moving parts. They can be even faster. They are still accessed using SCSI protocol that sends one command at a time. With NVMe (Non-Volatile Memory Express), a protocol that will be used to access SSDs via PCIe interface.
This is an excellent introduction to NVMe: NVMe for Absolute Beginners.
I took the Linux Kernel fundamentals course on Linkedin Learning during the Week of Learning. I went through the first three lessons. The last two deals with compiling the kernel. I skipped them as I had done some kernel compiling years ago and I won’t be doing them anytime soon.
These are my notes from the lessons:
I have always thought Virtual Filesystems like /proc and /sys are stored in memory, they are not. They are generated when asked for it. Each file and directory has associated function in the kernel that generates the content when you ask.
Continue reading “Notes from Linux Kernel Fundamentals course”
Systemd journal logs are by default not persistent. They are stored in memory (kernel ring buffer) are /run/log/journal. This means, journal logs are available only from the current boot.
# journalctl --list-boots
0 f27172ee431b4012af52b7623468e2fc Fri 2016-10-21 06:16:53 CDT—Fri 2016-10-21 06:17:22 CDT
Logs from previous boot are not available. However, since journal logs are forward to rsyslog are default, you can still see journal logs from previous boot from /var/log/messages. You will not be able to view logs from previous boots using the journalctl command. Continue reading “What’s new in RHEL7: Persistent journal log”
NTP service is provided by Chrony.
[root@rtfmp ~]# yum info chrony
Name : chrony
Arch : x86_64
Version : 2.1.1
Release : 1.el7.centos
Size : 280 k
Repo : base/7/x86_64
Summary : An NTP client/server
URL : http://chrony.tuxfamily.org
License : GPLv2
Description : A client/server for the Network Time Protocol, this program keeps
: your computer's clock accurate. It was specially designed to
: support systems with intermittent internet connections, but it
: also works well in permanently connected environments. It can use
: also hardware reference clocks, system real-time clock or manual
: input as time references.
If it is not installed, install it using Continue reading “What’s new in RHEL7: Chrony”