systat

Real-Time System Status for Mac/Linux.

Screen shot of i3wm on Linux. Three consoles/terminals in the left column, each running systat on a different host. The middle host/systat is a MacOS host.

Overview

This program refreshes the console/terminal/screen once per second and prints useful information about the system resources. Displayed are:

1. OS and Kernel version
2. Uptime and Load Average
3. CPU state (and per core if the console is tall enough)
4. Memory usage (RAM and Swap), free, buffers, etc.
5. Disk activity (per device) - bytes/IOs for read/write
6. Virtual Memory activity - paging, swapping info
7. Network activity per interface - read/write bytes/second, errors, etc.

The information printed is more detailed if there are enough lines in the terminal to print it. That is, if you make your console window tall enough, you will get CPU information for every core of your CPU. Otherwise, you only get the combined CPU state.

It is based on a Perl script I wrote many years ago for Linux that performs most of these functions. The Perl script requires you to install Term::Screen from CPAN.

The Perl script is loosely based upon the systat -vmstat command for BSD (FreeBSD at least).

The reason I rewrote systat in C++ is to make it portable between MacOS and Linux, and to assure it uses a minimal amount of resources itself. You don't want to be measuring systat performance while diagnosing a busy system! I also added the networking information, which was absent in the Perl script.

Building for MacOS

You can build the MacOS version:

cd c/mac
make
# to run it:
./systat
# to install it:
sudo make install

Building for Linux

The Linux version was built using vim and gnu make/Makefiles. To build it:

cd c/linux
make
# to run it:
./systat
# to install it:
make install

How it works

Both MacOS and Linux versions are structured in a similar manner and share the classes in the common/ directory. Using Makefile build, libcommon.a is built in common/, otherwise the classes are built and linked in, and no library is built.

One of the design goals is to make the program build with no prerequisites. You won't have to install ncurses or any other library. The Linux version links with no libraries other than the standard C++ ones. The Mac version has to link with various MacOS frameworks to access the needed APIs.

For each of the following classes, there is a global singleton instance, declared in the .cpp file for the class. I like it better to do:

console.println("hello, world");

instead of

Console::println("hello, world");

and I get to take advantage of the class constructors to initialize it all.

There are a few platform specific classes in the c/mac/ and c/linux/ directories. These directories should contain identical filenames/classes.

The main.cpp file is the main program. It basically calls each of the platform specific class' update() methods once per second. It then calls each of the platform specific class' print() methods.

The platform specific classes contain the business logic to obtain the useful information that is printed by systat. It took quite a bit of discovery to learn which /proc files to parse on Linux systems, and what OSX/Darwin API calls to make to get the desired information/samples.

The print() methods take a bool argument "test" that if set, the routine only returns the number of lines that would be printed. This is so the main program can "fit" the displayed information to the console, based upon its height. The fit process involves condensing the various output (what the classes would print), so the informatioj00jn printed does fit the console. It is possible to make the console too small - this is a TODO to handle this case.

Console Class

The Console class implements an api to address the cursor, control the display modes (e.g. bold, fg/bg colors, etc.), print output (printf format style), and clear lines/whole screen.

It is implemented to use ANSI escape sequences. This is lightweight, but probably not perfect. I tested using several terminal programs for Linux and iterm2 on Mac. It works fine.

This satisfies the design goal of not relying on some 3rd party library that would need to be installed as a dependency.

A SIGINT handler is installed to call the console's destructor, which restores the TTY to a sane state (e.g. enable cursor, default fg/bg colors, etc.).

The program does not do any keyboard I/O or interaction. To quit the program, hit ^C (Control+c).

Parser Class

This is only used by the Linux version, which mainly gets system information by parsing files in the /proc filesystem. Parser does a lot of the work, making the business logic for parsing these files rather elegant.

Log Class

If you include "../common/Log.h" in any of the .cpp/.h files, then there will be a global logger singleton. The constructor opens/creates /tmp/systat.log, which you can "tail -f" to see debug output. Logger.println(FORMAT, ...) to print debugging to the log file.

License

MIT License

Credits

Programmed by Mike Schwartz for Modus Create.
https://moduscreate.com