From 423ea1a5c47dc08b0f11fdbf57ea85f1fc6b4d72 Mon Sep 17 00:00:00 2001
From: Seth Hoenig <seth.a.hoenig@gmail.com>
Date: Wed, 24 Aug 2022 13:07:31 -0500
Subject: [PATCH] client/logmon: acquire executable in init block

This PR causes the logmon task runner to acquire the binary of the
Nomad executable in an 'init' block, so as to almost certainly get
the name while the nomad file still exists.

This is an attempt at fixing the case where a deleted Nomad file
(e.g. during upgrade) may be getting renamed with a mysterious
suffix first.

If this doesn't work, as a last resort we can literally just trim
the mystery string.

Fixes: #14079
---
 .changelog/14297.txt    |  3 +++
 client/logmon/plugin.go | 19 ++++++++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)
 create mode 100644 .changelog/14297.txt

diff --git a/.changelog/14297.txt b/.changelog/14297.txt
new file mode 100644
index 000000000..207eb3858
--- /dev/null
+++ b/.changelog/14297.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+client/logmon: fixed a bug where logmon cannot find nomad executable
+```
diff --git a/client/logmon/plugin.go b/client/logmon/plugin.go
index 5d97b751d..a21777357 100644
--- a/client/logmon/plugin.go
+++ b/client/logmon/plugin.go
@@ -5,22 +5,27 @@ import (
 	"os"
 	"os/exec"
 
-	hclog "github.com/hashicorp/go-hclog"
-	plugin "github.com/hashicorp/go-plugin"
+	"github.com/hashicorp/go-hclog"
+	"github.com/hashicorp/go-plugin"
 	"github.com/hashicorp/nomad/client/logmon/proto"
 	"github.com/hashicorp/nomad/plugins/base"
 	"google.golang.org/grpc"
 )
 
+var bin = getBin()
+
+func getBin() string {
+	b, err := os.Executable()
+	if err != nil {
+		panic(err)
+	}
+	return b
+}
+
 // LaunchLogMon launches a new logmon or reattaches to an existing one.
 // TODO: Integrate with base plugin loader
 func LaunchLogMon(logger hclog.Logger, reattachConfig *plugin.ReattachConfig) (LogMon, *plugin.Client, error) {
 	logger = logger.Named("logmon")
-	bin, err := os.Executable()
-	if err != nil {
-		return nil, nil, err
-	}
-
 	conf := &plugin.ClientConfig{
 		HandshakeConfig: base.Handshake,
 		Plugins: map[string]plugin.Plugin{