feat(inputs.system): collect unique user count logged in (#12147)

plugins/inputs/system/README.md

@@ -28,6 +28,10 @@ The `n_users` field requires read access to `/var/run/utmp`, and may require the
 `telegraf` user to be added to the `utmp` group on some systems. If this file
 does not exist `n_users` will be skipped.
 
+The `n_unique_users` shows the count of unique usernames logged in. This way if
+a user has multiple sessions open/started they would only get counted once. The
+same requirements for `n_users` apply.
+
 ## Metrics
 
 - system
@@ -36,6 +40,7 @@ does not exist `n_users` will be skipped.
     - load15 (float)
     - load5 (float)
     - n_users (integer)
+    - n_unique_users (integer)
     - n_cpus (integer)
     - uptime (integer, seconds)
     - uptime_format (string, deprecated in 1.10, use `uptime` field)

plugins/inputs/system/system.go

@@ -50,6 +50,7 @@ func (s *SystemStats) Gather(acc telegraf.Accumulator) error {
 	users, err := host.Users()
 	if err == nil {
 		fields["n_users"] = len(users)
+		fields["n_unique_users"] = findUniqueUsers(users)
 	} else if os.IsNotExist(err) {
 		s.Log.Debugf("Reading users: %s", err.Error())
 	} else if os.IsPermission(err) {
@@ -74,6 +75,17 @@ func (s *SystemStats) Gather(acc telegraf.Accumulator) error {
 	return nil
 }
 
+func findUniqueUsers(userStats []host.UserStat) int {
+	uniqueUsers := make(map[string]bool)
+	for _, userstat := range userStats {
+		if _, ok := uniqueUsers[userstat.User]; !ok {
+			uniqueUsers[userstat.User] = true
+		}
+	}
+
+	return len(uniqueUsers)
+}
+
 func formatUptime(uptime uint64) string {
 	buf := new(bytes.Buffer)
 	w := bufio.NewWriter(buf)

plugins/inputs/system/system_test.go

@@ -0,0 +1,65 @@
+package system
+
+import (
+	"testing"
+
+	"github.com/shirou/gopsutil/v3/host"
+	"github.com/stretchr/testify/require"
+)
+
+func TestUniqueUsers(t *testing.T) {
+	tests := []struct {
+		name     string
+		expected int
+		data     []host.UserStat
+	}{
+		{
+			name:     "single entry",
+			expected: 1,
+			data: []host.UserStat{
+				{User: "root"},
+			},
+		},
+		{
+			name:     "emptry entry",
+			expected: 0,
+			data:     []host.UserStat{},
+		},
+		{
+			name:     "all duplicates",
+			expected: 1,
+			data: []host.UserStat{
+				{User: "root"},
+				{User: "root"},
+				{User: "root"},
+			},
+		},
+		{
+			name:     "all unique",
+			expected: 3,
+			data: []host.UserStat{
+				{User: "root"},
+				{User: "ubuntu"},
+				{User: "ec2-user"},
+			},
+		},
+		{
+			name:     "mix of dups",
+			expected: 3,
+			data: []host.UserStat{
+				{User: "root"},
+				{User: "ubuntu"},
+				{User: "ubuntu"},
+				{User: "ubuntu"},
+				{User: "ec2-user"},
+				{User: "ec2-user"},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := findUniqueUsers(tt.data)
+			require.Equal(t, tt.expected, actual, tt.name)
+		})
+	}
+}