目录

获取进程正在监听的信号信息

Linux下的信号列表

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# 通过kill -l命令可以查看系统中的信号列表
root@027d6e9f6190:/opt# kill -l
 1) SIGHUP	 2) SIGINT	 3) SIGQUIT	 4) SIGILL	 5) SIGTRAP
 6) SIGABRT	 7) SIGBUS	 8) SIGFPE	 9) SIGKILL	10) SIGUSR1
11) SIGSEGV	12) SIGUSR2	13) SIGPIPE	14) SIGALRM	15) SIGTERM
16) SIGSTKFLT	17) SIGCHLD	18) SIGCONT	19) SIGSTOP	20) SIGTSTP
21) SIGTTIN	22) SIGTTOU	23) SIGURG	24) SIGXCPU	25) SIGXFSZ
26) SIGVTALRM	27) SIGPROF	28) SIGWINCH	29) SIGIO	30) SIGPWR
31) SIGSYS	34) SIGRTMIN	35) SIGRTMIN+1	36) SIGRTMIN+2	37) SIGRTMIN+3
38) SIGRTMIN+4	39) SIGRTMIN+5	40) SIGRTMIN+6	41) SIGRTMIN+7	42) SIGRTMIN+8
43) SIGRTMIN+9	44) SIGRTMIN+10	45) SIGRTMIN+11	46) SIGRTMIN+12	47) SIGRTMIN+13
48) SIGRTMIN+14	49) SIGRTMIN+15	50) SIGRTMAX-14	51) SIGRTMAX-13	52) SIGRTMAX-12
53) SIGRTMAX-11	54) SIGRTMAX-10	55) SIGRTMAX-9	56) SIGRTMAX-8	57) SIGRTMAX-7
58) SIGRTMAX-6	59) SIGRTMAX-5	60) SIGRTMAX-4	61) SIGRTMAX-3	62) SIGRTMAX-2
63) SIGRTMAX-1	64) SIGRTMAX

检查进程正在监听的信号的实现原理

在Linux下, 您可以找到您的进程的PID, 然后查看/proc/$PID/status 它包含描述哪些信号:

  • 被阻止(SigBlk)
  • 被忽略(SigIgn)
  • 被捕获(SigCgt)
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# cat /proc/1/status
...
SigBlk: 0000000000000000
SigIgn: fffffffe57f0d8fc
SigCgt: 00000000280b2603
...
右边的数字是位掩码。如果将其从十六进制转换为二进制,则每个1位代表捕获的信号,从1开始从右到左计数。因此,通过解释SigCgt行,我们可以看到我的init进程正在捕获以下信号:

00000000280b2603 ==> 101000000010110010011000000011
                     | |       | ||  |  ||       |`->  1 = SIGHUP
                     | |       | ||  |  ||       `-->  2 = SIGINT
                     | |       | ||  |  |`----------> 10 = SIGUSR1
                     | |       | ||  |  `-----------> 11 = SIGSEGV
                     | |       | ||  `--------------> 14 = SIGALRM
                     | |       | |`-----------------> 17 = SIGCHLD
                     | |       | `------------------> 18 = SIGCONT
                     | |       `--------------------> 20 = SIGTSTP
                     | `----------------------------> 28 = SIGWINCH
                     `------------------------------> 30 = SIGPWR
                     
例如:
root@027d6e9f6190:/# cat /proc/1/status | grep SigCgt
SigCgt:	0000000000014002

1. 将0x0000000000014002转换为二进制10100000000000010
2. 二进制从右向左看置1的位置
3. 最终得到: 2、15、17的位置被置1了
4. 查看信号列表中2、15、17所代表的信号信息

2  SIGINT
15 SIGTERM
17 SIGCHLD

结论: 1号进程捕获了SIGINT、SIGTERM和SIGCHLD这三种信号

检查进程正在监听的信号的工具

有大佬将上述手工解析的过程编写成了python脚本

psig.py

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# -*- coding: utf-8 -*-
#
# Print human-readable signal info for specified linux process(es).
# By default this prints all signal info from /proc/<PID>/status.
#
# Author: Erik Weathers

from __future__ import print_function
import argparse
import collections
import errno
import glob
import re
import sys

def error(*objs):
    print("ERROR: ", *objs, file=sys.stderr)

# Signal names for signal numbers.
#
# % kill -l
#  1) SIGHUP	 2) SIGINT	 3) SIGQUIT	 4) SIGILL	 5) SIGTRAP
#  6) SIGABRT	 7) SIGBUS	 8) SIGFPE	 9) SIGKILL	10) SIGUSR1
# 11) SIGSEGV	12) SIGUSR2	13) SIGPIPE	14) SIGALRM	15) SIGTERM
# 16) SIGSTKFLT	17) SIGCHLD	18) SIGCONT	19) SIGSTOP	20) SIGTSTP
# 21) SIGTTIN	22) SIGTTOU	23) SIGURG	24) SIGXCPU	25) SIGXFSZ
# 26) SIGVTALRM	27) SIGPROF	28) SIGWINCH	29) SIGIO	30) SIGPWR
# 31) SIGSYS	34) SIGRTMIN	35) SIGRTMIN+1	36) SIGRTMIN+2	37) SIGRTMIN+3
# 38) SIGRTMIN+4	39) SIGRTMIN+5	40) SIGRTMIN+6	41) SIGRTMIN+7	42) SIGRTMIN+8
# 43) SIGRTMIN+9	44) SIGRTMIN+10	45) SIGRTMIN+11	46) SIGRTMIN+12	47) SIGRTMIN+13
# 48) SIGRTMIN+14	49) SIGRTMIN+15	50) SIGRTMAX-14	51) SIGRTMAX-13	52) SIGRTMAX-12
# 53) SIGRTMAX-11	54) SIGRTMAX-10	55) SIGRTMAX-9	56) SIGRTMAX-8	57) SIGRTMAX-7
# 58) SIGRTMAX-6	59) SIGRTMAX-5	60) SIGRTMAX-4	61) SIGRTMAX-3	62) SIGRTMAX-2
# 63) SIGRTMAX-1	64) SIGRTMAX

SIGNALS = {
    1: 'SIGHUP',
    2: 'SIGINT',
    3: 'SIGQUIT',
    4: 'SIGILL',
    5: 'SIGTRAP',
    6: 'SIGABRT',
    7: 'SIGBUS',
    8: 'SIGFPE',
    9: 'SIGKILL',
    10: 'SIGUSR1',
    11: 'SIGSEGV',
    12: 'SIGUSR2',
    13: 'SIGPIPE',
    14: 'SIGALRM',
    15: 'SIGTERM',
    16: 'SIGSTKFLT',
    17: 'SIGCHLD',
    18: 'SIGCONT',
    19: 'SIGSTOP',
    20: 'SIGTSTP',
    21: 'SIGTTIN',
    22: 'SIGTTOU',
    23: 'SIGURG',
    24: 'SIGXCPU',
    25: 'SIGXFSZ',
    26: 'SIGVTALRM',
    27: 'SIGPROF',
    28: 'SIGWINCH',
    29: 'SIGIO',
    30: 'SIGPWR',
    31: 'SIGSYS',
    34: 'SIGRTMIN',
    35: 'SIGRTMIN+1',
    36: 'SIGRTMIN+2',
    37: 'SIGRTMIN+3',
    38: 'SIGRTMIN+4',
    39: 'SIGRTMIN+5',
    40: 'SIGRTMIN+6',
    41: 'SIGRTMIN+7',
    42: 'SIGRTMIN+8',
    43: 'SIGRTMIN+9',
    44: 'SIGRTMIN+10',
    45: 'SIGRTMIN+11',
    46: 'SIGRTMIN+12',
    47: 'SIGRTMIN+13',
    48: 'SIGRTMIN+14',
    49: 'SIGRTMIN+15',
    50: 'SIGRTMAX-14',
    51: 'SIGRTMAX-13',
    52: 'SIGRTMAX-12',
    53: 'SIGRTMAX-11',
    54: 'SIGRTMAX-10',
    55: 'SIGRTMAX-9',
    56: 'SIGRTMAX-8',
    57: 'SIGRTMAX-7',
    58: 'SIGRTMAX-6',
    59: 'SIGRTMAX-5',
    60: 'SIGRTMAX-4',
    61: 'SIGRTMAX-3',
    62: 'SIGRTMAX-2',
    63: 'SIGRTMAX-1',
    64: 'SIGRTMAX'
}

def signal_bitmask_to_human_readable(bitmask_string):
    signals = []
    bitmask = int(bitmask_string, 16)
    for signum, signame in SIGNALS.iteritems():
        if (bitmask & (1 << (signum - 1))) != 0:
            signals.append(signame)
    return ','.join(signals)

# Return a dict of signal information scraped from the following
# lines from /proc/<PID>/status:
#
# SigQ: 2/58791
# SigPnd: 0000000000000000
# ShdPnd: 0000000000000000
# SigBlk: 0000000000000000
# SigIgn: 0000000000001000
# SigCgt: 00000001a0016623
def obtain_signal_info(pid):
    signal_info = collections.OrderedDict()
    with open("/proc/%d/status" % pid) as f:
        pattern = r"^(?:Sig|ShdPnd).*$"
        for line in re.findall(pattern, f.read(), flags=re.MULTILINE):
            parts = line.split(":", 1)
            if parts:
                signal_info[parts[0]] = parts[1].strip()
    return signal_info

SIGNAL_OPTIONS = {
    'SigQ':   'signals_queued',
    'SigPnd': 'pending_signals_for_thread',
    'ShdPnd': 'pending_signals_for_whole_process',
    'SigBlk': 'blocked_signals',
    'SigIgn': 'ignored_signals',
    'SigCgt': 'caught_signals'
}

def option_enabled(args, key):
    if 'all_info' in vars(args):
        return True
    if SIGNAL_OPTIONS[key]:
        if vars(args)[SIGNAL_OPTIONS[key]]:
            return True
    return False

OUTPUT_HEADERS = {
    'SigQ':   'Signals Queued',
    'SigPnd': 'Signals Pending',
    'ShdPnd': 'Signals Pending (Shared)',
    'SigBlk': 'Signals Blocked',
    'SigIgn': 'Signals Ignored',
    'SigCgt': 'Signals Caught'
}

def print_signal_info(args, pid, max_pid_length):
    output_fmt = "[%%0%ss] %%s: %%s" % max_pid_length
    for k,v in obtain_signal_info(pid).iteritems():
        if option_enabled(args, k):
            print(output_fmt % \
                (pid,
                 OUTPUT_HEADERS[k],
                 v if k == 'SigQ' else signal_bitmask_to_human_readable(v)))

# Support hosts with a modified max PID number.
def get_max_pid_length():
    pid_max = ''
    with open('/proc/sys/kernel/pid_max') as f:
        pid_max = f.read()
    return len(pid_max)

def main(args):
    max_pid_length = get_max_pid_length()

    # Single PID?
    if args.pid and not args.thread_info:
        try:
            print_signal_info(args, args.pid, max_pid_length)
        except IOError as e:
            if e.errno == 2:
                sys.exc_clear()
                error("PID %s does not exist" % args.pid)
                sys.exit(1)
            else:
                raise
    else:
        # All Processes, all Threads, or all Threads of a single Process
        try:
            if args.all_pids:
                glob_pattern = '/proc/[0-9]*'
            elif args.all_threads:
                glob_pattern = '/proc/[0-9]*/task/[0-9]*'
            elif args.thread_info and args.pid:
                glob_pattern = ('/proc/%d/task/[0-9]*' % args.pid)
            else:
                raise "Unexpected arguments specified, cannot proceed."

            for proc_entry in glob.glob(glob_pattern):
                pid = int(proc_entry.split('/')[-1])
                print_signal_info(args, pid, max_pid_length)
        except IOError as e:
            if e.errno == errno.ENOENT:
                # Swallow exception for the PID dir not existing, since it's likely
                # some enumerated processes will die before we can print their info.
                sys.exc_clear()
            else:
                raise

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Print human-readable signal info for specified process. By default all signal info is printed.')
    group = parser.add_mutually_exclusive_group(required=True)
    group.add_argument('-p', '--pid', type=int, help='Process ID')
    group.add_argument('-a', '--all-pids', action='store_true', help='Print signal info for all Processes')
    group.add_argument('-T', '--all-threads', action='store_true', help='Print signal info for all Threads')
    parser.add_argument('-t', '--thread-info', action='store_true', help='Print signal info for all Threads of the specified PID')
    parser.add_argument('-A', '--all-info', action='store_true', default=True, help='Print all signal info for specified PID(s). Implies -b,-i,-c,-l,-P,-q.')
    parser.add_argument('-b', '--blocked-signals', action='store_true', help='Print human-readable SigBlk from specified PID(s)')
    parser.add_argument('-i', '--ignored-signals', action='store_true', help='Print human-readable SigIgn from specified PID(s)')
    parser.add_argument('-c', '--caught-signals', action='store_true', help='Print human-readable SigCgt from specified PID(s)')
    parser.add_argument('-l', '--pending-signals-for-thread', action='store_true', help='Print human-readable SigPnd from specified PID(s)')
    parser.add_argument('-P', '--pending-signals-for-whole-process', action='store_true', help='Print human-readable ShdPnd from specified PID(s)')
    parser.add_argument('-q', '--signals-queued', action='store_true', help='Print SigQ from specified PID(s)')
    args = parser.parse_args()
    if (args.blocked_signals or args.ignored_signals or args.caught_signals or args.pending_signals_for_thread or
        args.pending_signals_for_whole_process or args.signals_queued):
        vars(args).pop('all_info')
    if (args.thread_info and not args.pid):
        error("must specify a PID when using -t / --thread-info")
        sys.exit(1)
    main(args)

运行效果:

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root@027d6e9f6190:/opt# python psig.py -p 1
[     1] Signals Queued: 3/31702
[     1] Signals Pending: 
[     1] Signals Pending (Shared): SIGCHLD
[     1] Signals Blocked: SIGCHLD
[     1] Signals Ignored: SIGQUIT
[     1] Signals Caught: SIGINT,SIGTERM,SIGCHLD

参考资料