walt-log-echo logging tool

walt-log-echo is a logging tool provided on all nodes. It allows to emit loglines. For more info about WalT logging in general, see walt help show logging.

Basic usage

You can run walt-log-echo like this:

[node]$ walt-log-echo <stream-name> <log-line>

This will emit a new <log-line> attached to logstream <stream-name>. You can obviously call this in the experiment scripts you run on nodes.

Advanced usage and performance tips

If you want to emit many log lines, you should consider using walt-log-cat instead. (see walt help show log-cat)

If you have means to record precise event timestamps (e.g. network timestamps), you can specify them by using option --timestamp:

[node]$ walt-log-echo --timestamp <ts> <stream-name> <log-line>

The <ts> value must be a UNIX timestamp, i.e. a floating point number of seconds since the ‘EPOCH’ (january 1, 1970). Without this option, the timestamp recorded will be the current time when walt-log-echo is run.

Simple example

I first run this in a first terminal:

$ walt log show --realtime

This will catch all loglines emitted from my nodes. (see walt help show log-realtime for more info)

Then, on a second terminal:

$ walt node shell node1
Caution: changes outside /persist will be lost on next node reboot.
Run 'walt help show shells' for more info.

root@node1:~# walt-log-echo 'exp1' 'this is a logline of exp1'

And immediately the logline is catched on first terminal:

$ walt log show --realtime
17:35:53.147851 node1.exp1 -> this is a logline of exp1