31

I know that with ps I can see the list or tree of the current processes running in the system. But what I want to achieve is to "follow" the new processes that are created when using the computer.

As analogy, when you use tail -f to follow the new contents appended to a file or to any input, then I want to keep a follow list of the process that are currently being created.

Is this even posible?

28

If kprobes are enabled in the kernel you can use execsnoop from perf-tools:

In first terminal:

% while true; do uptime; sleep 1; done

In another terminal:

% git clone https://github.com/brendangregg/perf-tools.git
% cd perf-tools
% sudo ./execsnoop
Tracing exec()s. Ctrl-C to end.
Instrumenting sys_execve
   PID   PPID ARGS
 83939  83937 cat -v trace_pipe
 83938  83934 gawk -v o=1 -v opt_name=0 -v name= -v opt_duration=0 [...]
 83940  76640 uptime
 83941  76640 sleep 1
 83942  76640 uptime
 83943  76640 sleep 1
 83944  76640 uptime
 83945  76640 sleep 1
^C
Ending tracing...
  • 2
    For new kernel versions (>= 4.17 if I understand correctly) on x84_64, Gregg's perf-tools no longer work - they run but there are no reports at all as it instruments an unused call. According to Gregg's comments elsewhere, the correct solution for kernels >= 4.7, is to use the BPF implementation in the BPF Compiler Collection available here: github.com/iovisor/bcc#tools and on Ubuntu and modern linuxes as bpfcc-tools. – Guss Jan 15 at 12:43
7

The easiest way is to enable system call auditing

See the following link for details,

Does anyone know a simple way to monitor root process spawn | Server Fault

If you're monitoring all processes, just remove the -F uid=0 part

Logs are written to /var/log/audit/audit.log

  • None of those 3 links answers my question. The first two are about coding something to resolve this and the last one does not answer neither. What I am asking is about some command and not writing some piece of code – Pablo Matias Gomez Feb 5 '16 at 16:46
  • @PabloMatíasGomez updated – daisy Feb 5 '16 at 16:48
3

CONFIG_PROC_EVENTS=y

Sample session:

$ su
# ./proc_events.out &
set mcast listen ok
# sleep 2 & sleep 1 &
fork: parent tid=48 pid=48 -> child tid=56 pid=56
fork: parent tid=48 pid=48 -> child tid=57 pid=57
exec: tid=57 pid=57
exec: tid=56 pid=56
exit: tid=57 pid=57 exit_code=0
exit: tid=56 pid=56 exit_code=0

CONFIG_PROC_EVENTS exposes the events to userland via a netlink socket.

proc_events.c

#define _XOPEN_SOURCE 700
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include <linux/cn_proc.h>
#include <signal.h>
#include <errno.h>
#include <stdbool.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

static volatile bool need_exit = false;

static int nl_connect()
{
    int rc;
    int nl_sock;
    struct sockaddr_nl sa_nl;

    nl_sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
    if (nl_sock == -1) {
        perror("socket");
        return -1;
    }
    sa_nl.nl_family = AF_NETLINK;
    sa_nl.nl_groups = CN_IDX_PROC;
    sa_nl.nl_pid = getpid();
    rc = bind(nl_sock, (struct sockaddr *)&sa_nl, sizeof(sa_nl));
    if (rc == -1) {
        perror("bind");
        close(nl_sock);
        return -1;
    }
    return nl_sock;
}

static int set_proc_ev_listen(int nl_sock, bool enable)
{
    int rc;
    struct __attribute__ ((aligned(NLMSG_ALIGNTO))) {
        struct nlmsghdr nl_hdr;
        struct __attribute__ ((__packed__)) {
            struct cn_msg cn_msg;
            enum proc_cn_mcast_op cn_mcast;
        };
    } nlcn_msg;

    memset(&nlcn_msg, 0, sizeof(nlcn_msg));
    nlcn_msg.nl_hdr.nlmsg_len = sizeof(nlcn_msg);
    nlcn_msg.nl_hdr.nlmsg_pid = getpid();
    nlcn_msg.nl_hdr.nlmsg_type = NLMSG_DONE;

    nlcn_msg.cn_msg.id.idx = CN_IDX_PROC;
    nlcn_msg.cn_msg.id.val = CN_VAL_PROC;
    nlcn_msg.cn_msg.len = sizeof(enum proc_cn_mcast_op);

    nlcn_msg.cn_mcast = enable ? PROC_CN_MCAST_LISTEN : PROC_CN_MCAST_IGNORE;

    rc = send(nl_sock, &nlcn_msg, sizeof(nlcn_msg), 0);
    if (rc == -1) {
        perror("netlink send");
        return -1;
    }

    return 0;
}

static int handle_proc_ev(int nl_sock)
{
    int rc;
    struct __attribute__ ((aligned(NLMSG_ALIGNTO))) {
        struct nlmsghdr nl_hdr;
        struct __attribute__ ((__packed__)) {
            struct cn_msg cn_msg;
            struct proc_event proc_ev;
        };
    } nlcn_msg;
    while (!need_exit) {
        rc = recv(nl_sock, &nlcn_msg, sizeof(nlcn_msg), 0);
        if (rc == 0) {
            /* shutdown? */
            return 0;
        } else if (rc == -1) {
            if (errno == EINTR) continue;
            perror("netlink recv");
            return -1;
        }
        switch (nlcn_msg.proc_ev.what) {
            case PROC_EVENT_NONE:
                printf("set mcast listen ok\n");
                break;
            case PROC_EVENT_FORK:
                printf("fork: parent tid=%d pid=%d -> child tid=%d pid=%d\n",
                        nlcn_msg.proc_ev.event_data.fork.parent_pid,
                        nlcn_msg.proc_ev.event_data.fork.parent_tgid,
                        nlcn_msg.proc_ev.event_data.fork.child_pid,
                        nlcn_msg.proc_ev.event_data.fork.child_tgid);
                break;
            case PROC_EVENT_EXEC:
                printf("exec: tid=%d pid=%d\n",
                        nlcn_msg.proc_ev.event_data.exec.process_pid,
                        nlcn_msg.proc_ev.event_data.exec.process_tgid);
                break;
            case PROC_EVENT_UID:
                printf("uid change: tid=%d pid=%d from %d to %d\n",
                        nlcn_msg.proc_ev.event_data.id.process_pid,
                        nlcn_msg.proc_ev.event_data.id.process_tgid,
                        nlcn_msg.proc_ev.event_data.id.r.ruid,
                        nlcn_msg.proc_ev.event_data.id.e.euid);
                break;
            case PROC_EVENT_GID:
                printf("gid change: tid=%d pid=%d from %d to %d\n",
                        nlcn_msg.proc_ev.event_data.id.process_pid,
                        nlcn_msg.proc_ev.event_data.id.process_tgid,
                        nlcn_msg.proc_ev.event_data.id.r.rgid,
                        nlcn_msg.proc_ev.event_data.id.e.egid);
                break;
            case PROC_EVENT_EXIT:
                printf("exit: tid=%d pid=%d exit_code=%d\n",
                        nlcn_msg.proc_ev.event_data.exit.process_pid,
                        nlcn_msg.proc_ev.event_data.exit.process_tgid,
                        nlcn_msg.proc_ev.event_data.exit.exit_code);
                break;
            default:
                printf("unhandled proc event\n");
                break;
        }
    }

    return 0;
}

static void on_sigint(__attribute__ ((unused)) int unused)
{
    need_exit = true;
}

int main()
{
    int nl_sock;
    int rc = EXIT_SUCCESS;

    signal(SIGINT, &on_sigint);
    siginterrupt(SIGINT, true);
    nl_sock = nl_connect();
    if (nl_sock == -1)
        exit(EXIT_FAILURE);
    rc = set_proc_ev_listen(nl_sock, true);
    if (rc == -1) {
        rc = EXIT_FAILURE;
        goto out;
    }
    rc = handle_proc_ev(nl_sock);
    if (rc == -1) {
        rc = EXIT_FAILURE;
        goto out;
    }
    set_proc_ev_listen(nl_sock, false);
out:
    close(nl_sock);
    exit(rc);
}

GitHub upsatream, code adapted from: https://bewareofgeek.livejournal.com/2945.html

I don't think however that you can you get process data such as UID and process arguments because exec_proc_event contains so little data: https://github.com/torvalds/linux/blob/v4.16/include/uapi/linux/cn_proc.h#L80 We could try to immediately read it from /proc, but there is a risk that the process finished and another one took its PID, so it wouldn't be reliable.

Tested on Ubuntu 17.10, which has CONFIG_PROC_EVENTS=y enabled by default.

2

You can apparently follow a process using strace. If you know the PID of the process then you can do:

strace -o strace-<pid>.out -f -p <pid>

Notice the -f switch. It will help you to follow newly created processes that are descendants of the process whose PID was used in the command, above. For information on strace see this question.

  • Apparently you were meaning to attach to the init process, with pid=1, right? Unfortunately it doesn't work, I don't see in the output any creation of new processes, and the number of lines is a few dozens, whilst the current pid for new processes went through a few hundreds. – Hi-Angel Oct 30 '17 at 8:33
0

You can use forkstat as stated here: https://stackoverflow.com/a/40532202/781153

Install with: apt-get install forkstat

And just run: forkstat

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