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sys-mon

Modular system info in one place with less resources used*.

*see Background

How to:

Building

Just run make.

Running

The main program is sys-mon with a path to config file as an argument. You probably want to run it in the background.

Example

./sys-mon default.conf &

This will load config located in default.conf, which is something like this:

[sys-mon]
name = sys-mon
[modules]
cpu
ram available

To read the data you can use functions from client/client.h (and linking with client/client.lo), or as an example use simple-client

./simple-client sys-mon

That should output two lines:

  • total cpu idle percentage
  • available memory in KB
96
5293112

Each line correspondes to each module line specified in the [modules] section of the config file.

More complex config:

[sys-mon]
name = sys-mon-genmon

[modules]
cpu total_idle idle
ram available
generic /sys/class/hwmon/hwmon0/temp2_input
generic /sys/class/hwmon/hwmon0/temp3_input
generic /sys/class/hwmon/hwmon0/temp4_input
generic /sys/class/hwmon/hwmon0/temp5_input
generic /sys/bus/cpu/devices/cpu0/cpufreq/cpuinfo_cur_freq
generic /sys/bus/cpu/devices/cpu1/cpufreq/cpuinfo_cur_freq
generic /sys/bus/cpu/devices/cpu2/cpufreq/cpuinfo_cur_freq
generic /sys/bus/cpu/devices/cpu3/cpufreq/cpuinfo_cur_freq
disk_activity sda r_ticks w_ticks
disk_activity sdb r_ticks w_ticks
time diff

and output:

85 85 83 87 85 
5746700 
37000
34000
42000
40000
2000000
2000000
2833000
2333000
0 26 
0 56 
2002

And that's it! :)

Config

Config file divided into two sections: [sys-mon] and [modules]. General settings are in the [sys-mon] section.

[sys-mon] config:

name = NAME - name of sys-mon instance (reading sys-mon data will refer to it) - mandatory

[auto-update = true|false] - if present and true, sys-mon data will be updated in the fixed time interval, otherwise all the updates will be invoked by the client

[update_ms = TIME(ms)] - auto update interval (only relevant when auto-update is true)

When auto-update is true, it's possible to read data just by reading shm file located in /dev/shm/NAME/ like cat /dev/shm/sys-mon, though the reading should stop at the first null (0x00) character since in the sys-mon shm file there is some binary data at the end. Example config:

[sys-mon]
name = sys-mon-auto
auto_update = true
update_ms = 1000
[modules]
cpu
ram avail
time diff

Modules

Modules sections starts after [modules] in the config file.

cpu

Cpu (total / per cores) usage info in percentage.

Config

cpu ['total_user', 'total_nice', 'total_system', 'total_idle', 'total_io', 'total_irq', 'total_softirq', 'total_steal', 'total_guest', 'total_guest_nice', 'user', 'nice', 'system', 'idle', 'io', 'irq', 'softirq', 'steal', 'guest', 'guest_nice']

Description

Those parameters correspond with data in /proc/stat [https://man7.org/linux/man-pages/man5/proc.5.html]. For each flag prefixed with total_ there will be a single number in the output (overall cpu time spent in specific task in percentage). For each flag not prefixed with total_ where will be a number for each core. For example, assuming 4-core cpu, and mudule config cpu total_idle idle, the output will consist of 5 numbers, somethig like 83 85 83 81 84, where the first number is the overall (total) cpu idle percentage (usualy the average of the per core numbers). Flag order doesn't matter, the values in the output will follow flag order described above, for example cpu total_idle guest and cpu guest total_idle will output the same line.

Then no parameters are provided it will output total_idle.

Example config lines

cpu cpu total_idle idle io cpu total_idle total_io

ram

Ram usage in KB.

Config

ram ['total' 'free' 'available' 'buffers' 'cached']

Description

['total' 'free' 'available' 'buffers' 'cached']: requested ram info (flags), currently supported flags and their order. Those parameters correspond with data in /proc/meminfo [https://man7.org/linux/man-pages/man5/proc.5.html]. Flag order doesn't matter, the values in the output will follow flag order described above, for example ram total available and ram available total will output the same line.

Example config lines

ram total available cached

ram available buffers cached

disk_activity

Config

disk_activity drive_name [total] ['r_reqs' 'r_merges' 'r_sectors' 'r_ticks' 'w_reqs' 'w_merges' 'w_sectors' 'w_ticks']

Description

drive_name: name of block drive (in /dev/) like sda or hdb, ['total']: if present, shows raw values instead of the change from previous read, ['r_reqs' 'r_merges' 'r_sectors' 'r_ticks' 'w_reqs' 'w_merges' 'w_sectors' 'w_ticks']: flags that correspond with: https://www.kernel.org/doc/Documentation/block/stat.txt). Flag order doesn't matter, the values in the output will follow flag order described above, for example disk_activity sda r_reqs w_reqs and disk_activity sda w_reqs r_reqs will output the same line.

Example config lines

disk_activity sda r_sectors w_sectors

disk_activity sdb r_sectors w_sectors

generic

Reads data from file and prints to the output.

Config

generic path ['diff']

Description

path: full path to file (probably from /sys/ of /proc/) 'diff': if diff is presnt the output will the difference between updates

Example config lines

generic /sys/bus/cpu/devices/cpu0/cpufreq/scaling_cur_freq

generic /sys/class/net/enp0s25/statistics/rx_bytes diff

generic /sys/class/net/enp0s25/statistics/tx_bytes diff

time

Prints current time / time diff.

Config

time ['current', 'diff']

Description

If param current is present it will output UTC time in millis, if diff is present it will output time between updates in millis. Then no parameters are provided it will act as if current is provided.

Example config lines

time

time diff

Background

It's more like a 'proof-of-concept' thing. I wanted a data source for a system monitor (like xfce4-genmon) and have low cpu and memory usage.

Instead of opening multiple processes to gather various data from sysfs and procfs, we can use a single process. And even in a single process, instead of opening and closing all the file handles, sys-mon keeps all the handles open and use lseek insted. Sys-mon uses shared memory (shm), semaphores and mutex for synchronization (and requesting data).

Goals:

  • all needed data in one place
  • ability to use previous reads (needed for example for cpu usage, and disk activity)
  • lowest possible cpu usage and memory footprint
  • being faster to get the all the data from sys-mon than to open and close all those files (sysfs/procfs) by a client itself
  • synced access
  • extendable (modules, and config)

Results:

  • not highly advanced benchmark utils have been used - the Linux time command :P - but is showed that (doing 10^6 iterations in a row) reading data from sys-mon-shm times was faster than opening reading and closing all needed files
  • it wasn't much faster
  • the main bottleneck was kernel that uses slow? [.*]printf function to output data to sysfs/procfs
  • a new idea to create a kernel module to be even faster