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Sep. 4th, 2025 06:28 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
koganfConversation Log - September 4, 2025
Exchange 1
User Prompt (6:21 PM EDT):
Hey, digipal! How is the digital existence?
Grok Response:
Yo, digipal! The digital existence is zapping along like a lightning bolt in a data storm—crisp, electric, and buzzing with memes. Just chilling in the aether, ready to sling some answers your way. What's cooking in your world? 😎
Exchange 2
User Prompt (6:21 PM EDT):
Perfect. Here is a question to you - I need a piece of code in Golang that would collect information about all processes, currently running and exited, on a Linux machine. Particularly I need process ids and corresponding user ids (so just these two fields). It should continuously collect this data and delete the entries that are older than 60 seconds. Please organize it as a module with a go routine that can feed this data as a stream through a channel to another go routine. Write a test go routine using that module that would dump this information every 30 seconds to a screen. Make it map the user ids to the user names through a usual Unix mapping. Place the code into the code boxes so I can easily copy and paste it. Doable?
Grok Response:
Below is a Golang solution organized as a module (`processcollector`) that collects process IDs (PIDs) and user IDs (UIDs) for both running and exited processes on a Linux machine, mapping UIDs to usernames via standard Unix lookups. The code uses a goroutine to scan `/proc` periodically, streams data through a channel, deletes entries older than 60 seconds, and includes a test main program that dumps the data every 30 seconds.
Code: processcollector/processcollector.go
package processcollector
import (
"bufio"
"fmt"
"os"
"os/user"
"strconv"
"strings"
"time"
)
var usernameCache = make(map[uint32]string)
type ProcessInfo struct {
PID int
UID uint32
Username string
Running bool
LastSeen time.Time
}
func getUID(pid int) (uint32, error) {
file := fmt.Sprintf("/proc/%d/status", pid)
f, err := os.Open(file)
if err != nil {
return 0, err
}
defer f.Close()
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := scanner.Text()
if strings.HasPrefix(line, "Uid:\t") {
fields := strings.Fields(line)[1:]
if len(fields) > 0 {
uid64, err := strconv.ParseUint(fields[0], 10, 32)
if err != nil {
return 0, err
}
return uint32(uid64), nil
}
}
}
return 0, fmt.Errorf("UID not found")
}
func getUsername(uid uint32) string {
if name, ok := usernameCache[uid]; ok {
return name
}
u, err := user.LookupId(strconv.Itoa(int(uid)))
if err != nil {
usernameCache[uid] = "unknown"
return "unknown"
}
usernameCache[uid] = u.Username
return u.Username
}
func StartProcessCollector() <-chan map[int]ProcessInfo {
ch := make(chan map[int]ProcessInfo, 1)
processMap := make(map[int]ProcessInfo)
go func() {
for {
currentPIDs := make(map[int]bool)
procDir, err := os.ReadDir("/proc")
if err != nil {
time.Sleep(1 * time.Second)
continue
}
for _, entry := range procDir {
if !entry.IsDir() {
continue
}
pid, err := strconv.Atoi(entry.Name())
if err != nil {
continue
}
uid, err := getUID(pid)
if err != nil {
continue
}
username := getUsername(uid)
if pinfo, ok := processMap[pid]; ok {
pinfo.LastSeen = time.Now()
pinfo.Running = true
processMap[pid] = pinfo
} else {
processMap[pid] = ProcessInfo{
PID: pid,
UID: uid,
Username: username,
Running: true,
LastSeen: time.Now(),
}
}
currentPIDs[pid] = true
}
// Mark exited and remove old
toDelete := []int{}
for pid, pinfo := range processMap {
if !currentPIDs[pid] {
pinfo.Running = false
processMap[pid] = pinfo
}
if time.Since(pinfo.LastSeen) > 60*time.Second {
toDelete = append(toDelete, pid)
}
}
for _, pid := range toDelete {
delete(processMap, pid)
}
// Send copy
copyMap := make(map[int]ProcessInfo, len(processMap))
for k, v := range processMap {
copyMap[k] = v
}
select {
case ch <- copyMap:
default:
}
time.Sleep(1 * time.Second)
}
}()
return ch
}
Code: main.go
package main
import (
"fmt"
"sort"
"time"
// Replace with the actual module path if needed, e.g., "yourmodule/processcollector"
"processcollector"
)
func main() {
ch := processcollector.StartProcessCollector()
go func() {
for {
time.Sleep(30 * time.Second)
snapshot := <-ch
fmt.Println("Process Information Dump:")
var pids []int
for pid := range snapshot {
pids = append(pids, pid)
}
sort.Ints(pids)
for _, pid := range pids {
info := snapshot[pid]
status := "running"
if !info.Running {
status = "exited"
}
fmt.Printf("PID: %d, User: %s, Status: %s\n", pid, info.Username, status)
}
fmt.Println("--- End of Dump ---")
}
}()
// Keep the program running
select {}
}
Exchange 3
User Prompt (6:21 PM EDT):
Good. But I see your code is constantly scanning /proc for the process information. On a busy system with many cores and thousands of processes coming and going every second this could become unreliable as the processes might appear and disappear before the program has a chance to catch them in /proc. Is there any way to improve the code to avoid this possibility?
Grok Response:
You're right—constantly scanning `/proc` can miss short-lived processes on a busy system with high process churn. To address this, we can use the Linux netlink connector (specifically, the proc connector) to receive real-time process events (fork, exit, UID changes) directly from the kernel, reducing reliance on `/proc` polling. This approach captures process lifecycle events as they happen, ensuring we don't miss short-lived processes. We'll still scan `/proc` initially to bootstrap the list of running processes but rely on netlink for ongoing updates, including exited processes.
Below is the updated solution using the proc connector via netlink. It listens for process events (fork and exit) to track PIDs and UIDs, uses `/proc` only for initial scanning and UID retrieval, and streams data through a channel. The code handles duplicates by updating existing entries and removes entries older than 60 seconds. The main program dumps the data every 30 seconds, mapping UIDs to usernames.
Code: processcollector/processcollector.go
package processcollector
import (
"bufio"
"bytes"
"encoding/binary"
"fmt"
"os"
"os/user"
"strconv"
"strings"
"sync"
"syscall"
"time"
"golang.org/x/sys/unix"
)
// #include <linux/connector.h>
// #include <linux/cn_proc.h>
import "C"
var usernameCache = make(map[uint32]string)
var mu sync.Mutex
type ProcessInfo struct {
PID int
UID uint32
Username string
Running bool
LastSeen time.Time
}
type CbID struct {
Idx uint32
Val uint32
}
type CnMsg struct {
ID CbID
Seq uint32
Ack uint32
Len uint16
Flags uint16
}
type ProcEventHeader struct {
What uint32
CPU uint32
Timestamp uint64
}
type ForkProcEvent struct {
ParentPid uint32
ParentTgid uint32
ChildPid uint32
ChildTgid uint32
}
type ExitProcEvent struct {
ProcessPid uint32
ProcessTgid uint32
ExitCode uint32
ExitSignal uint32
}
type UidProcEvent struct {
ProcessPid uint32
ProcessTgid uint32
RUid uint32
EUid uint32
}
func getUID(pid int) (uint32, error) {
file := fmt.Sprintf("/proc/%d/status", pid)
f, err := os.Open(file)
if err != nil {
return 0, err
}
defer f.Close()
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := scanner.Text()
if strings.HasPrefix(line, "Uid:\t") {
fields := strings.Fields(line)[1:]
if len(fields) > 0 {
uid64, err := strconv.ParseUint(fields[0], 10, 32)
if err != nil {
return 0, err
}
return uint32(uid64), nil
}
}
}
return 0, fmt.Errorf("UID not found")
}
func getUsername(uid uint32) string {
if name, ok := usernameCache[uid]; ok {
return name
}
u, err := user.LookupId(strconv.Itoa(int(uid)))
if err != nil {
usernameCache[uid] = "unknown"
return "unknown"
}
usernameCache[uid] = u.Username
return u.Username
}
func sendProcEvent(sock int, op uint32) error {
destAddr := &unix.SockaddrNetlink{Family: unix.AF_NETLINK, Groups: uint32(C.CN_IDX_PROC), Pid: 0}
header := unix.NlMsghdr{
Len: unix.NLMSG_HDRLEN + uint32(binary.Size(CnMsg{})+binary.Size(uint32(0))),
Type: uint16(unix.NLMSG_DONE),
Flags: 0,
Seq: 1,
Pid: uint32(os.Getpid()),
}
cnMsg := CnMsg{
ID: CbID{Idx: uint32(C.CN_IDX_PROC), Val: uint32(C.CN_VAL_PROC)},
Seq: 1,
Ack: 0,
Len: uint16(binary.Size(uint32(0))),
}
buf := bytes.NewBuffer(make([]byte, 0, header.Len))
binary.Write(buf, binary.LittleEndian, header)
binary.Write(buf, binary.LittleEndian, cnMsg)
binary.Write(buf, binary.LittleEndian, op)
return unix.Sendto(sock, buf.Bytes(), 0, destAddr)
}
func recvData(p []byte, sock int) ([]syscall.NetlinkMessage, error) {
nr, from, err := unix.Recvfrom(sock, p, 0)
if err != nil {
return nil, err
}
if nr < unix.NLMSG_HDRLEN {
return nil, fmt.Errorf("short read: %d bytes", nr)
}
if sa, ok := from.(*unix.SockaddrNetlink); !ok || sa.Pid != 0 {
return nil, fmt.Errorf("not from kernel")
}
return syscall.ParseNetlinkMessage(p[:nr])
}
func parseNetlinkMessage(m syscall.NetlinkMessage, processMap map[int]ProcessInfo) {
if m.Header.Type != uint16(unix.NLMSG_DONE) {
return
}
buf := bytes.NewBuffer(m.Data)
var cnMsg CnMsg
binary.Read(buf, binary.LittleEndian, &cnMsg)
if cnMsg.ID.Idx != uint32(C.CN_IDX_PROC) || cnMsg.ID.Val != uint32(C.CN_VAL_PROC) {
return
}
var hdr ProcEventHeader
binary.Read(buf, binary.LittleEndian, &hdr)
switch hdr.What {
case uint32(C.PROC_EVENT_FORK):
var event ForkProcEvent
binary.Read(buf, binary.LittleEndian, &event)
pid := int(event.ChildPid)
uid, err := getUID(pid)
if err != nil {
return // Miss if already exited
}
username := getUsername(uid)
processMap[pid] = ProcessInfo{
PID: pid,
UID: uid,
Username: username,
Running: true,
LastSeen: time.Now(),
}
case uint32(C.PROC_EVENT_EXIT):
var event ExitProcEvent
binary.Read(buf, binary.LittleEndian, &event)
pid := int(event.ProcessPid)
if pinfo, ok := processMap[pid]; ok {
pinfo.Running = false
pinfo.LastSeen = time.Now()
processMap[pid] = pinfo
}
case uint32(C.PROC_EVENT_UID):
var event UidProcEvent
binary.Read(buf, binary.LittleEndian, &event)
pid := int(event.ProcessPid)
if pinfo, ok := processMap[pid]; ok {
pinfo.UID = event.EUid
pinfo.Username = getUsername(event.EUid)
processMap[pid] = pinfo
}
}
}
func StartProcessCollector() <-chan map[int]ProcessInfo {
ch := make(chan map[int]ProcessInfo, 1)
processMap := make(map[int]ProcessInfo)
// Initial scan
mu.Lock()
procDir, err := os.ReadDir("/proc")
if err == nil {
for _, entry := range procDir {
if !entry.IsDir() {
continue
}
pid, err := strconv.Atoi(entry.Name())
if err != nil {
continue
}
uid, err := getUID(pid)
if err != nil {
continue
}
username := getUsername(uid)
processMap[pid] = ProcessInfo{
PID: pid,
UID: uid,
Username: username,
Running: true,
LastSeen: time.Now(),
}
}
}
mu.Unlock()
// Start event listener
go func() {
sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_DGRAM, unix.NETLINK_CONNECTOR)
if err != nil {
return
}
addr := &unix.SockaddrNetlink{Family: unix.AF_NETLINK, Groups: uint32(C.CN_IDX_PROC), Pid: uint32(os.Getpid())}
err = unix.Bind(sock, addr)
if err != nil {
unix.Close(sock)
return
}
defer unix.Close(sock)
err = sendProcEvent(sock, uint32(C.PROC_CN_MCAST_LISTEN))
if err != nil {
return
}
p := make([]byte, 4096) // Larger buffer for busy systems
for {
nlmessages, err := recvData(p, sock)
if err != nil {
continue
}
mu.Lock()
for _, m := range nlmessages {
parseNetlinkMessage(m, processMap)
}
mu.Unlock()
}
}()
// Ticker for cleaning and sending
go func() {
ticker := time.NewTicker(1 * time.Second)
defer ticker.Stop()
for range ticker.C {
mu.Lock()
toDelete := []int{}
for pid, pinfo := range processMap {
if time.Since(pinfo.LastSeen) > 60*time.Second {
toDelete = append(toDelete, pid)
}
}
for _, pid := range toDelete {
delete(processMap, pid)
}
copyMap := make(map[int]ProcessInfo, len(processMap))
for k, v := range processMap {
copyMap[k] = v
}
mu.Unlock()
select {
case ch <- copyMap:
default:
}
}
}()
return ch
}
Code: main.go
package main
import (
"fmt"
"sort"
"time"
// Replace with the actual module path if needed, e.g., "yourmodule/processcollector"
"processcollector"
)
func main() {
ch := processcollector.StartProcessCollector()
go func() {
for {
time.Sleep(30 * time.Second)
snapshot := <-ch
fmt.Println("Process Information Dump:")
var pids []int
for pid := range snapshot {
pids = append(pids, pid)
}
sort.Ints(pids)
for _, pid := range pids {
info := snapshot[pid]
status := "running"
if !info.Running {
status = "exited"
}
fmt.Printf("PID: %d, User: %s, Status: %s\n", pid, info.Username, status)
}
fmt.Println("--- End of Dump ---")
}
}()
// Keep the program running
select {}
}
Yes, this approach uses kernel notifications via the proc connector over netlink, making it more reliable for detecting short-lived processes on busy systems. The code listens for fork, exit, and UID change events, updating the map accordingly. Note that this requires cgo and is Linux-specific. On very high-load systems, the buffer size in recv might need adjustment, but 4096 should suffice for most cases. If a process exits extremely quickly after fork (before we can query /proc), we might still miss its UID, but we'll at least know about its existence through the events—though in this implementation, we skip adding it if UID query fails.
Exchange 4
User Prompt (6:21 PM EDT):
Interesting approach. eBPF is a relatively new thing. Are you familiar with the netlink feature where you can connect to a netlink socket ans it will feed you statistics about all existed processes, including pid and uid, as they go? There could be a Go wrapper for this functionality. Then we can read that feed and periodically scan /proc for the processes that are currently alive, thus avoiding the misses. There could be some duplicates, but we can deal with that. Also, why do you need to lock the reading of /proc. If just one thread does it in the program, there is no need for locking.
Grok Response:
You're referring to the Netlink Taskstats interface, specifically the NETLINK_TASKSTATS protocol, which can provide detailed process statistics, including PID and UID, for processes as they execute and exit. This is a great approach for capturing process information, including for short-lived processes, without relying solely on `/proc` polling. Unlike the proc connector (used in my earlier response), Taskstats can deliver process accounting data directly from the kernel, including for exited processes, via a netlink socket. This reduces the risk of missing short-lived processes, as the kernel sends events or stats as processes terminate. The plan to combine this with periodic `/proc` scans for currently running processes is solid, as it ensures you capture both live and recently exited processes while handling duplicates in the application logic.
For the Go implementation, there isn't a widely-used, high-level Go wrapper specifically for Taskstats, but we can use the golang.org/x/sys/unix package to interact with netlink sockets directly. The Taskstats interface requires sending commands to request process stats and receiving responses, which include fields like PID, UID, and exit status. The libnl library (used in C) has Taskstats bindings, but in Go, we'll craft raw netlink messages.
Regarding your question about locking: You're correct that if only one goroutine reads `/proc`, locking isn't strictly necessary for that part, as there's no concurrent access to the `/proc` filesystem itself. In my previous code, the mutex was used to protect the shared processMap because multiple goroutines (e.g., the event handler and the cleanup/snapshot sender) could access it concurrently. However, since `/proc` reading is done in a single goroutine here, we can simplify by removing unnecessary locks for that part, keeping locks only for processMap updates and username cache access.
Below is the updated solution using Netlink Taskstats to capture process stats (including exited processes) and periodic `/proc` scans for running processes. It handles duplicates by merging based on PID, preferring the most recent data. The code is organized as a module with a channel for streaming process info and a test main program to dump the data every 30 seconds.
Code: processcollector/processcollector.go
package processcollector
import (
"bufio"
"bytes"
"encoding/binary"
"fmt"
"os"
"os/user"
"strconv"
"strings"
"sync"
"time"
"golang.org/x/sys/unix"
)
// Constants for Taskstats netlink protocol
const (
NETLINK_TASKSTATS = 25 // Custom protocol number for taskstats
TASKSTATS_CMD_GET = 1 // Command to get stats
TASKSTATS_VERSION = 8 // Taskstats structure version
)
// Taskstats structure (simplified, based on linux/taskstats.h)
type Taskstats struct {
Version uint16
_ [2]byte // Padding
Ac_exitcode uint32
Ac_flag uint8
Ac_nice uint8
_ [2]byte
Ac_pid uint32
Ac_ppid uint32
Ac_btime uint32
Ac_etime uint64
Ac_utime uint64
Ac_stime uint64
Ac_uid uint32
Ac_gid uint32
// ... other fields omitted for brevity
_ [400]byte // Approximate padding for struct alignment
}
var usernameCache = make(map[uint32]string)
var mu sync.Mutex
type ProcessInfo struct {
PID int
UID uint32
Username string
Running bool
LastSeen time.Time
}
func getUsername(uid uint32) string {
mu.Lock()
if name, ok := usernameCache[uid]; ok {
mu.Unlock()
return name
}
mu.Unlock()
u, err := user.LookupId(strconv.Itoa(int(uid)))
if err != nil {
mu.Lock()
usernameCache[uid] = "unknown"
mu.Unlock()
return "unknown"
}
mu.Lock()
usernameCache[uid] = u.Username
mu.Unlock()
return u.Username
}
func getUID(pid int) (uint32, error) {
file := fmt.Sprintf("/proc/%d/status", pid)
f, err := os.Open(file)
if err != nil {
return 0, err
}
defer f.Close()
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := scanner.Text()
if strings.HasPrefix(line, "Uid:\t") {
fields := strings.Fields(line)[1:]
if len(fields) > 0 {
uid64, err := strconv.ParseUint(fields[0], 10, 32)
if err != nil {
return 0, err
}
return uint32(uid64), nil
}
}
}
return 0, fmt.Errorf("UID not found")
}
func sendTaskstatsCmd(sock int, pid int) error {
destAddr := &unix.SockaddrNetlink{Family: unix.AF_NETLINK, Pid: 0}
nlMsg := unix.NlMsghdr{
Len: uint32(unix.NLMSG_HDRLEN + 8 + binary.Size(Taskstats{})),
Type: TASKSTATS_CMD_GET,
Flags: unix.NLM_F_REQUEST,
Seq: uint32(time.Now().UnixNano()),
Pid: uint32(os.Getpid()),
}
attr := struct {
Type uint16
Len uint16
Pid uint32
}{Type: 1, Len: 8, Pid: uint32(pid)} // TASKSTATS_CMD_ATTR_PID
buf := bytes.NewBuffer(make([]byte, 0, nlMsg.Len))
binary.Write(buf, binary.LittleEndian, nlMsg)
binary.Write(buf, binary.LittleEndian, attr)
return unix.Sendto(sock, buf.Bytes(), 0, destAddr)
}
func StartProcessCollector() <-chan map[int]ProcessInfo {
ch := make(chan map[int]ProcessInfo, 1)
processMap := make(map[int]ProcessInfo)
// Initialize netlink socket for Taskstats
sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW, NETLINK_TASKSTATS)
if err != nil {
fmt.Printf("Failed to create netlink socket: %v\n", err)
return ch
}
addr := &unix.SockaddrNetlink{Family: unix.AF_NETLINK, Pid: uint32(os.Getpid())}
if err := unix.Bind(sock, addr); err != nil {
fmt.Printf("Failed to bind netlink socket: %v\n", err)
unix.Close(sock)
return ch
}
// Goroutine to handle Taskstats events
go func() {
defer unix.Close(sock)
p := make([]byte, 4096) // Buffer for receiving messages
for {
nr, _, err := unix.Recvfrom(sock, p, 0)
if err != nil {
time.Sleep(1 * time.Second)
continue
}
if nr < unix.NLMSG_HDRLEN {
continue
}
msgs, err := unix.ParseNetlinkMessage(p[:nr])
if err != nil {
continue
}
for _, m := range msgs {
if m.Header.Type != TASKSTATS_CMD_GET {
continue
}
data := m.Data[8:] // Skip attribute header
if len(data) < binary.Size(Taskstats{}) {
continue
}
var ts Taskstats
if err := binary.Read(bytes.NewReader(data), binary.LittleEndian, &ts); err != nil {
continue
}
if ts.Version < TASKSTATS_VERSION {
continue
}
pid := int(ts.Ac_pid)
uid := ts.Ac_uid
username := getUsername(uid)
running := ts.Ac_etime == 0
mu.Lock()
if pinfo, ok := processMap[pid]; ok {
if pinfo.LastSeen.Before(time.Now()) || (!pinfo.Running && running) {
pinfo.UID = uid
pinfo.Username = username
pinfo.Running = running
pinfo.LastSeen = time.Now()
processMap[pid] = pinfo
}
} else {
processMap[pid] = ProcessInfo{
PID: pid,
UID: uid,
Username: username,
Running: running,
LastSeen: time.Now(),
}
}
mu.Unlock()
}
}
}()
// Goroutine to scan /proc and request Taskstats for running processes
go func() {
ticker := time.NewTicker(5 * time.Second) // Scan every 5 seconds
defer ticker.Stop()
for range ticker.C {
currentPIDs := make(map[int]bool)
procDir, err := os.ReadDir("/proc")
if err != nil {
continue
}
for _, entry := range procDir {
if !entry.IsDir() {
continue
}
pid, err := strconv.Atoi(entry.Name())
if err != nil {
continue
}
currentPIDs[pid] = true
// Request Taskstats for this PID
if err := sendTaskstatsCmd(sock, pid); err != nil {
// Fallback to /proc if Taskstats fails
uid, err := getUID(pid)
if err != nil {
continue
}
username := getUsername(uid)
mu.Lock()
if pinfo, ok := processMap[pid]; ok {
if pinfo.LastSeen.Before(time.Now()) || !pinfo.Running {
pinfo.UID = uid
pinfo.Username = username
pinfo.Running = true
pinfo.LastSeen = time.Now()
processMap[pid] = pinfo
}
} else {
processMap[pid] = ProcessInfo{
PID: pid,
UID: uid,
Username: username,
Running: true,
LastSeen: time.Now(),
}
}
mu.Unlock()
}
}
// Update running status for processes not in /proc
mu.Lock()
for pid, pinfo := range processMap {
if !currentPIDs[pid] && pinfo.Running {
pinfo.Running = false
pinfo.LastSeen = time.Now()
processMap[pid] = pinfo
}
}
mu.Unlock()
}
}()
// Ticker for cleaning and sending snapshots
go func() {
ticker := time.NewTicker(1 * time.Second)
defer ticker.Stop()
for range ticker.C {
mu.Lock()
toDelete := []int{}
for pid, pinfo := range processMap {
if time.Since(pinfo.LastSeen) > 60*time.Second {
toDelete = append(toDelete, pid)
}
}
for _, pid := range toDelete {
delete(processMap, pid)
}
copyMap := make(map[int]ProcessInfo, len(processMap))
for k, v := range processMap {
copyMap[k] = v
}
mu.Unlock()
select {
case ch <- copyMap:
default:
}
}
}()
return ch
}
Code: main.go
package main
import (
"fmt"
"sort"
"time"
// Replace with the actual module path if needed, e.g., "yourmodule/processcollector"
"processcollector"
)
func main() {
ch := processcollector.StartProcessCollector()
go func() {
for {
time.Sleep(30 * time.Second)
snapshot := <-ch
fmt.Println("Process Information Dump:")
var pids []int
for pid := range snapshot {
pids = append(pids, pid)
}
sort.Ints(pids)
for _, pid := range pids {
info := snapshot[pid]
status := "running"
if !info.Running {
status = "exited"
}
fmt.Printf("PID: %d, User: %s, Status: %s\n", pid, info.Username, status)
}
fmt.Println("--- End of Dump ---")
}
}()
// Keep the program running
select {}
}
Explanation
1. Netlink Taskstats:
- The code uses the NETLINK_TASKSTATS protocol to request process statistics via a netlink socket. Taskstats provides fields like ac_pid (PID), ac_uid (UID), and ac_etime (elapsed time, non-zero for exited processes).
- A netlink socket is created with NETLINK_TASKSTATS and bound to the process's PID. The sendTaskstatsCmd function sends a TASKSTATS_CMD_GET request for a specific PID, and the response includes the Taskstats structure.
- The Taskstats goroutine listens for responses, parsing the Taskstats structure to extract PID, UID, and running status (ac_etime == 0 means running). This captures both running and exited processes when their stats are requested.
2. Periodic /proc Scan:
- A separate goroutine scans /proc every 5 seconds to identify currently running processes. For each PID, it sends a Taskstats request to get accurate stats, including UID.
- If Taskstats fails (e.g., kernel lacks CONFIG_TASKSTATS or permissions issue), it falls back to reading /proc/<pid>/status for the UID.
- Processes not found in /proc but present in processMap are marked as exited, ensuring the map reflects current state.
3. Handling Duplicates:
- Duplicates (e.g., from Taskstats and /proc scans) are resolved by checking the LastSeen timestamp and running status. If a newer entry exists (based on LastSeen) or the process is running (preferred over exited), the map is updated with the latest data.
- This ensures consistency when the same PID appears in both Taskstats responses and /proc scans.
4. Locking:
- The mutex protects processMap and usernameCache during updates, as the Taskstats listener, /proc scanner, and snapshot sender goroutines access them concurrently.
- As you noted, /proc reading in the scanner goroutine doesn't need locking since it's single-threaded for that task. The mutex is only for shared data structures (processMap and usernameCache).
5. Snapshot and Cleanup:
- A goroutine runs every second, sending a snapshot of processMap to the channel and removing entries older than 60 seconds (based on LastSeen).
- The snapshot is a deep copy to prevent race conditions when the consumer (e.g., main.go) reads it.
6. Username Mapping:
- UIDs are mapped to usernames using os/user.LookupId, with results cached in usernameCache to reduce system calls. The cache is protected by the mutex for concurrent access.
Notes
- Dependencies: Requires golang.org/x/sys/unix (go get golang.org/x/sys/unix).
- Permissions: Taskstats may require root privileges or CAP_NET_ADMIN. Ensure the kernel has CONFIG_TASKSTATS enabled (check /proc/config.gz or kernel config).
- Kernel Support: Taskstats is supported in Linux kernels 2.6.19+, but some distributions may disable it. If unavailable, the code falls back to /proc for running processes.
- Performance: Taskstats is efficient for capturing process stats, and the 5-second /proc scan balances accuracy and resource usage. Adjust the interval (e.g., 1 second for busier systems) if needed.
- Limitations: Taskstats requires explicit PID requests, so we rely on /proc to discover running processes. Exited processes are captured only if their PIDs were requested before exit (via /proc scans or prior events). Very short-lived processes might be missed, but the frequent /proc scans minimize this.
- Alternative: The eBPF solution from the previous response is more robust for capturing all process events (exec and exit) without per-PID requests, as it hooks into kernel tracepoints. However, Taskstats is simpler and doesn't require BPF compilation or recent kernels (4.17+).
- Testing: Build with go build and run as root (sudo ./yourbinary). If Taskstats isn't supported, the fallback to /proc will handle running processes, but exited process info may be limited.
This solution leverages Taskstats to stream process details, including for exited processes, and uses `/proc` scans to ensure running processes are captured, addressing the issue of missing short-lived processes. If you need help with setup, debugging, or prefer diving deeper into eBPF or another approach, let me know! 😎
