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/*
Package journald offers Go implementation of systemd Journal's native API for logging. Key features are:
- based on connection-less socket
- work with messages of any size and type
- client can use any number of separation sockets
Let's look at what the journald provides as Go APIs for logging:
package main
import (
"github.com/ssgreg/journald"
)
func main() {
journald.Print(journald.PriorityInfo, "Hello World!")
}
The JSON representation of the journal entry this generates:
{
"PRIORITY": "6",
"MESSAGE": "Hello World!",
"_PID": "3965",
"_COMM": "simple",
...
}
The primary reason for using the Journal's native logging APIs is a not just the source code location however: it is to allow passing additional structured log messages from the program into the journal. This additional log data may the be used to search the journal for, is available for consumption for other programs, and might help the administrator to track down issues beyond what is expressed in the human readable message text. Here's and example how to do that with journals.Send:
package main
import (
"os"
"runtime"
"github.com/ssgreg/journald"
)
func main() {
journald.Send("Hello World!", journald.PriorityInfo, map[string]interface{}{
"HOME": os.Getenv("HOME"),
"TERM": os.Getenv("TERM"),
"N_GOROUTINE": runtime.NumGoroutine(),
"N_CPUS": runtime.NumCPU(),
"TRACE": runtime.ReadTrace(),
})
}
This will write a log message to the journal much like the earlier examples. However, this times a few additional, structured fields are attached:
{
"PRIORITY": "6",
"MESSAGE": "Hello World!",
"HOME": "/root",
"TERM": "xterm",
"N_GOROUTINE": "2",
"N_CPUS": "4",
"TRACE": [103,111,32,49,46,56,32,116,114,97,99,101,0,0,0,0],
"_PID": "4037",
"_COMM": "send",
...
}
Our structured message includes six fields. The first thow we passed are well-known fields:
1. MESSAGE= is the actual human readable message part of the structured message.
2. PRIORITY= is the numeric message priority value as known from BSD syslog formatted as an integer string.
Applications may relatively freely define additional fields as they see fit (we defined four pretty arbitrary ones in our example). A complete list of the currently well-known fields is available here: https://www.freedesktop.org/software/systemd/man/systemd.journal-fields.html
For more details visit https://github.com/ssgreg/journald-send
Thanks to http://0pointer.de/blog/ for the inspiration.
*/
package journald
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