fix(inputs.procstat): Resolve remote usernames on Posix systems

Author: srebhan

plugins/inputs/procstat/README.md

@@ -147,6 +147,13 @@ Some files or directories may require elevated permissions. As such a user may
 need to provide telegraf with higher levels of permissions to access and produce
 metrics.
 
+### Remote users on Posix systems
+
+To resolve usernames of processes owned by remote users e.g. LDAP or NIS the
+plugin relies on the `id` command. This command must be available on the system,
+in the PATH and executable by Telegraf, otherwise the username cannot be
+resolved and the user-ID is used instead.
+
 ## Metrics
 
 For descriptions of these tags and fields, consider reading one of the

plugins/inputs/procstat/filter.go

@@ -139,8 +139,8 @@ func (f *filter) applyFilter() ([]processGroup, error) {
 		for _, p := range g.processes {
 			// Users
 			if f.filterUser != nil {
-				if username, err := p.Username(); err != nil || !f.filterUser.Match(username) {
-					// Errors can happen if we don't have permissions or the process no longer exists
+				if username := username(p); username != "" || !f.filterUser.Match(username) {
+					// This can happen if we don't have permissions or the process no longer exists
 					continue
 				}
 			}

plugins/inputs/procstat/native_finder.go

@@ -21,12 +21,9 @@ func (*NativeFinder) uid(user string) ([]pid, error) {
 		return dst, err
 	}
 	for _, p := range procs {
-		username, err := p.Username()
-		if err != nil {
-			// skip, this can be caused by the pid no longer exists, or you don't have permissions to access it
-			continue
-		}
-		if username == user {
+		// Skip this process if we cannot determine the username e.g. due
+		// to the fact that the process no longer exists.
+		if username := username(p); username != "" && username == user {
 			dst = append(dst, pid(p.Pid))
 		}
 	}

plugins/inputs/procstat/os_linux.go

@@ -7,6 +7,8 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"os/exec"
+	"os/user"
 	"strconv"
 	"strings"
 	"syscall"
@@ -25,6 +27,32 @@ func processName(p *gopsprocess.Process) (string, error) {
 	return p.Exe()
 }
 
+func username(p *gopsprocess.Process) string {
+	// Use the local lookup
+	n, err := p.Username()
+	if err == nil {
+		return n
+	}
+
+	// Exit on errors other than unknown user-ID
+	var uerr user.UnknownUserIdError
+	if !errors.As(err, &uerr) {
+		return ""
+	}
+
+	// Try to run the `id` command on the UID of the process to resolve remote
+	// users such as LDAP or NIS.
+	uid := strconv.Itoa(int(uerr))
+	buf, err := exec.Command("id", "-nu", uid).Output()
+	if n := strings.TrimSpace(string(buf)); err == nil && n != "" {
+		return n
+	}
+
+	// We were either not able to run the command or the user cannot be
+	// resolved so just return the user ID instead.
+	return uid
+}
+
 func queryPidWithWinServiceName(_ string) (uint32, error) {
 	return 0, errors.New("os not supporting win_service option")
 }

plugins/inputs/procstat/os_others.go

@@ -4,6 +4,10 @@ package procstat
 
 import (
 	"errors"
+	"os/exec"
+	"os/user"
+	"strconv"
+	"strings"
 	"syscall"
 
 	gopsnet "github.com/shirou/gopsutil/v4/net"
@@ -14,6 +18,32 @@ func processName(p *gopsprocess.Process) (string, error) {
 	return p.Exe()
 }
 
+func username(p *gopsprocess.Process) string {
+	// Use the local lookup
+	n, err := p.Username()
+	if err == nil {
+		return n
+	}
+
+	// Exit on errors other than unknown user-ID
+	var uerr user.UnknownUserIdError
+	if !errors.As(err, &uerr) {
+		return ""
+	}
+
+	// Try to run the `id` command on the UID of the process to resolve remote
+	// users such as LDAP or NIS.
+	uid := strconv.Itoa(int(uerr))
+	buf, err := exec.Command("id", "-nu", uid).Output()
+	if n := strings.TrimSpace(string(buf)); err == nil && n != "" {
+		return n
+	}
+
+	// We were either not able to run the command or the user cannot be
+	// resolved so just return the user ID instead.
+	return uid
+}
+
 func queryPidWithWinServiceName(string) (uint32, error) {
 	return 0, errors.New("os not supporting win_service option")
 }

plugins/inputs/procstat/os_windows.go

@@ -18,6 +18,13 @@ func processName(p *gopsprocess.Process) (string, error) {
 	return p.Name()
 }
 
+func username(p *gopsprocess.Process) string {
+	if n, err := p.Username(); err == nil {
+		return n
+	}
+	return ""
+}
+
 func getService(name string) (*mgr.Service, error) {
 	m, err := mgr.Connect()
 	if err != nil {

plugins/inputs/procstat/process.go

@@ -232,8 +232,7 @@ func (p *proc) metrics(prefix string, cfg *collectionConfig, t time.Time) ([]tel
 		}
 	}
 
-	user, err := p.Username()
-	if err == nil {
+	if user := username(p.Process); user != "" {
 		if cfg.tagging["user"] {
 			p.tags["user"] = user
 		} else {