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实际取消分叉进程

tag-icon • tag-icon process background-process debugging fork clone
实际取消分叉进程

我有一个可执行的二进制文件（无源），可以克隆（）。它没有打印任何东西，我认为孩子正在尝试打印任何东西，我希望它这样做。即使子进程实际上失败了，它也总是成功返回。我想要孩子的退货代码。提示也会立即返回，但我想要在前台运行的东西；要么通过神奇地取消分叉，要么等待子进程终止。

我能做些什么？仅Linux就可以了。

我尝试了这样的脚本，至少获得输出并留在前台：

thecmd &
daemon="$(pgrep -P $!)"
cat "/proc/$daemon/fd/2" >&2

但在我得到它之前，孩子可能会失败并且没有输出。

我试图获取守护进程和标准输出：

cmd &
daemon="$(pgrep -P $!)"
echo "daemon: $daemon"

echo "parent's stdout:"
readlink -f "/proc/$!/fd/1"
echo "child's stdout:"
readlink -f "/proc/$daemon/fd/1"

印刷：

daemon:
parent's stdout:
child's stdout:

这是strace -f子进程失败的输出（为什么没有 stderr？）：

23266 execve("/usr/local/sbin/tobiiusbserviced", ["/usr/local/sbin/tobiiusbserviced"], 0x7ffc21846b08 /* 17 vars */) = 0
23266 brk(NULL)                         = 0x2368000
23266 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/tls/haswell/x86_64/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/tls/haswell/x86_64", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/tls/haswell/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/tls/haswell", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/tls/x86_64/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/tls/x86_64", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/tls/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/tls", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/haswell/x86_64/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/haswell/x86_64", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/haswell/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/haswell", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/x86_64/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 stat("/usr/local/lib/tobiiusb/x86_64", 0x7ffdbcb20d80) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/libtobii_osal.so", O_RDONLY|O_CLOEXEC) = 3
23266 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@6\0\0\0\0\0\0"..., 832) = 832
23266 fstat(3, {st_mode=S_IFREG|0644, st_size=54270, ...}) = 0
23266 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa9213b8000
23266 mmap(NULL, 2141088, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa9211ad000
23266 mprotect(0x7fa9211b7000, 2093056, PROT_NONE) = 0
23266 mmap(0x7fa9213b6000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x9000) = 0x7fa9213b6000
23266 close(3)                          = 0
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/libtobii_libc.so", O_RDONLY|O_CLOEXEC) = 3
23266 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\"\0\0\0\0\0\0"..., 832) = 832
23266 fstat(3, {st_mode=S_IFREG|0644, st_size=56335, ...}) = 0
23266 mmap(NULL, 2161696, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa920f9d000
23266 mprotect(0x7fa920fa8000, 2093056, PROT_NONE) = 0
23266 mmap(0x7fa9211a7000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xa000) = 0x7fa9211a7000
23266 mmap(0x7fa9211a9000, 15392, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa9211a9000
23266 close(3)                          = 0
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/libudev.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
23266 fstat(3, {st_mode=S_IFREG|0644, st_size=81564, ...}) = 0
23266 mmap(NULL, 81564, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fa920f89000
23266 close(3)                          = 0
23266 openat(AT_FDCWD, "/usr/lib/libudev.so.1", O_RDONLY|O_CLOEXEC) = 3
23266 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200Y\0\0\0\0\0\0"..., 832) = 832
23266 fstat(3, {st_mode=S_IFREG|0755, st_size=158016, ...}) = 0
23266 mmap(NULL, 162056, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa920f61000
23266 mprotect(0x7fa920f66000, 135168, PROT_NONE) = 0
23266 mmap(0x7fa920f66000, 94208, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x5000) = 0x7fa920f66000
23266 mmap(0x7fa920f7d000, 36864, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c000) = 0x7fa920f7d000
23266 mmap(0x7fa920f87000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x25000) = 0x7fa920f87000
23266 close(3)                          = 0
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
23266 openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
23266 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@\177\2\0\0\0\0\0"..., 832) = 832
23266 fstat(3, {st_mode=S_IFREG|0755, st_size=12976264, ...}) = 0
23266 mmap(NULL, 1856160, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa920d9b000
23266 mmap(0x7fa920dc1000, 1351680, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7fa920dc1000
23266 mmap(0x7fa920f0b000, 311296, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x170000) = 0x7fa920f0b000
23266 mmap(0x7fa920f57000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bb000) = 0x7fa920f57000
23266 mmap(0x7fa920f5d000, 12960, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fa920f5d000
23266 close(3)                          = 0
23266 openat(AT_FDCWD, "/usr/local/lib/tobiiusb/libtobii_usb.so", O_RDONLY|O_CLOEXEC) = 3
23266 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\30\0\0\0\0\0\0"..., 832) = 832
23266 fstat(3, {st_mode=S_IFREG|0644, st_size=33286, ...}) = 0
23266 mmap(NULL, 2122072, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fa920b94000
23266 mprotect(0x7fa920b9a000, 2093056, PROT_NONE) = 0
23266 mmap(0x7fa920d99000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x5000) = 0x7fa920d99000
23266 close(3)                          = 0
23266 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa920b92000
23266 arch_prctl(ARCH_SET_FS, 0x7fa920b93040) = 0
23266 mprotect(0x7fa920f57000, 12288, PROT_READ) = 0
23266 mprotect(0x7fa920d99000, 4096, PROT_READ) = 0
23266 mprotect(0x7fa920f87000, 4096, PROT_READ) = 0
23266 mprotect(0x7fa9213b6000, 4096, PROT_READ) = 0
23266 mprotect(0x7fa9211a7000, 4096, PROT_READ) = 0
23266 mprotect(0x604000, 4096, PROT_READ) = 0
23266 mprotect(0x7fa9213e4000, 4096, PROT_READ) = 0
23266 munmap(0x7fa920f89000, 81564)     = 0
23266 clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fa920b93310) = 23267
23266 exit_group(0 <unfinished ...>
23267 umask(000 <unfinished ...>
23266 <... exit_group resumed>)         = ?
23267 <... umask resumed>)              = 022
23267 setsid( <unfinished ...>
23266 +++ exited with 0 +++
23267 <... setsid resumed>)             = 23267
23267 brk(NULL)                         = 0x2368000
23267 brk(0x2389000)                    = 0x2389000
23267 openat(AT_FDCWD, "/var/run/tobiiusb/tobiiusbservice.pid", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
23267 fstat(3, {st_mode=S_IFREG|0644, st_size=0, ...}) = 0
23267 write(3, "23267", 5)              = 5
23267 close(3)                          = 0
23267 rt_sigaction(SIGTERM, {sa_handler=0x4023e0, sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7fa920dd8000}, NULL, 8) = 0
23267 rt_sigaction(SIGUSR1, {sa_handler=0x402c70, sa_mask=[USR1], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7fa920dd8000}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
23267 rt_sigaction(SIGUSR2, {sa_handler=0x402d30, sa_mask=[USR2], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7fa920dd8000}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
23267 chdir("/")                        = 0
23267 close(0)                          = 0
23267 close(1)                          = 0
23267 close(2)                          = 0
23267 openat(AT_FDCWD, "/etc/udev/udev.conf", O_RDONLY|O_CLOEXEC) = 0
23267 fstat(0, {st_mode=S_IFREG|0644, st_size=49, ...}) = 0
23267 read(0, "# see udev.conf(5) for details\n\n"..., 4096) = 49
23267 read(0, "", 4096)                 = 0
23267 close(0)                          = 0
23267 access("/run/udev/control", F_OK) = 0
23267 socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT) = 0
23267 setsockopt(0, SOL_SOCKET, SO_ATTACH_FILTER, {len=10, filter=0x7ffdbcb20a20}, 16) = 0
23267 bind(0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=0x000002}, 12) = 0
23267 getsockname(0, {sa_family=AF_NETLINK, nl_pid=23267, nl_groups=0x000002}, [12]) = 0
23267 setsockopt(0, SOL_SOCKET, SO_PASSCRED, [1], 4) = 0
23267 openat(AT_FDCWD, "/sys/devices/system/cpu/online", O_RDONLY|O_CLOEXEC) = 1
23267 read(1, "0-3\n", 8192)            = 4
23267 close(1)                          = 0
23267 sched_get_priority_max(SCHED_FIFO) = 99
23267 sched_get_priority_min(SCHED_FIFO) = 1
23267 writev(2, [{iov_base="/usr/local/sbin/tobiiusbserviced", iov_len=32}, {iov_base=": ", iov_len=2}, {iov_base="symbol lookup error", iov_len=19}, {iov_base=": ", iov_len=2}, {iov_base="/usr/local/lib/tobiiusb/libtobii"..., iov_len=40}, {iov_base=": ", iov_len=2}, {iov_base="undefined symbol: pthread_create", iov_len=32}, {iov_base="", iov_len=0}, {iov_base="", iov_len=0}, {iov_base="\n", iov_len=1}], 10) = -1 EBADF (Bad file descriptor)
23267 exit_group(127)                   = ?
23267 +++ exited with 127 +++

答案1

  • 您的访问尝试 可能是徒劳的。/proc/pid/fd/N

  • 只要您对程序的唯一访问权限是黑盒，运行strace -f可能是您能做的最好的事情。 （然后strace在输出中搜索exit和write。）类似的选项是尝试在调试器下运行程序。如果您想自动化此操作，请尝试确定明确的需求，尽您所能，然后在遇到困难时提出新问题。

    也许最好的解决方案是获得白盒访问；即，获取源代码。使用反向编译器从二进制文件生成源代码可能是一种选择。

  • 查看strace您提供的输出，我们可以看到

    • 子进程使用文件描述符3写入“ 23267” /var/run/tobiiusb/tobiiusbservice.pid。这实际上是子进程的PID。
    • 它使用系统调用将“/usr/local/sbin/tobiiusbserviced：符号查找错误：/usr/local/lib/tobiiusb/libtobii…：未定义符号：pthread_create\n”写入文件描述符2 writev。上面字符串中的“...”并不是字面上的三个点，而是表示已被截断的文本，以防止输出过于冗长。要查看完整数据，请尝试将--verbose=write或--verbose='/write*'选项传递给 strace。和/或 --write=all（或 --write=0,1,2,3,4,5,6,7，如果“ all”不起作用）。
    • 上述错误消息没有出现在任何地方，因为程序之前已经关闭了文件描述符 0、1 和 2。
    • 正如您所怀疑的，子进程以状态 127 退出（使用exit_group系统调用）。

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