Telnet 从守护进程运行时无法正常运行

Posted 2023-03-16

【中文标题】Telnet 从守护进程运行时无法正常运行

【英文标题】：Telnet fails to run properly when run from daemon process

【发布时间】：2011-08-13 17:20:41

【问题描述】：

当我调用 telnet 从交互式 shell 连接到白天服务器时，它工作正常。但是，当从 cron 或某些 bash 守护进程运行的 shell 脚本发出相同的 telnet 调用时，它无法产生任何 otput。我跟踪了这​​两个电话，它们是：

成功者：

execve("/usr/bin/telnet", ["telnet", "192.168.0.11", "13"], [/* 24 vars */]) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x4000000, -1, 0) = 0x40005000
stat("/etc/ld.so.cache", st_mode=S_IFREG|0644, st_size=3128, ...) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
mmap2(NULL, 3128, PROT_READ, MAP_SHARED, 3, 0) = 0x40006000
close(3)                                = 0
stat("/etc/ld.so.preload", 0xbea5d8d4)  = -1 ENOENT (No such file or directory)
open("/lib/libc.so.0", O_RDONLY)        = 3
fstat(3, st_mode=S_IFREG|0755, st_size=324423, ...) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x4000000, -1, 0) = 0x40007000
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\320\253\0\0004\0\0\0\0"..., 4096) = 4096
mmap2(NULL, 376832, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4000e000
mmap2(0x4000e000, 319264, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0) = 0x4000e000
mmap2(0x40064000, 4935, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x4e) = 0x40064000
mmap2(0x40066000, 14712, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x40066000
close(3)                                = 0
munmap(0x40007000, 4096)                = 0
munmap(0x40006000, 3128)                = 0
stat("/lib/ld-uClibc.so.0", st_mode=S_IFREG|0755, st_size=20486, ...) = 0
mprotect(0x40064000, 4096, PROT_READ)   = 0
mprotect(0x4000c000, 4096, PROT_READ)   = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, B38400 opost isig icanon echo ...) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, B38400 opost isig icanon echo ...) = 0
getuid32()                              = 0
ioctl(0, TIOCGWINSZ, ws_row=55, ws_col=203, ws_xpixel=0, ws_ypixel=0) = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, B38400 opost isig icanon echo ...) = 0
brk(0)                                  = 0x91000
brk(0x92000)                            = 0x92000
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
connect(3, sa_family=AF_INET, sin_port=htons(13), sin_addr=inet_addr("192.168.0.11"), 16) = 0
setsockopt(3, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
rt_sigaction(SIGINT, 0x667c0, [INT], SA_RESTART|0x4000000, SIG_DFL, [], 0, 8) = 0
poll([fd=0, events=POLLIN, fd=3, events=POLLIN], 2, -1) = 1 ([fd=3, revents=POLLIN])
read(3, "Wed Apr 27 11:42:10 2011\r\n"..., 128) = 26
write(1, "Wed Apr 27 11:42:10 2011\r\n"..., 26) = 26
poll([fd=0, events=POLLIN, fd=3, events=POLLIN], 2, -1) = 1 ([fd=3, revents=POLLIN])
read(3, ""..., 128)                     = 0
write(1, "Connection closed by foreign host"..., 35) = 35
ioctl(0, SNDCTL_TMR_STOP or TCSETSW, B38400 opost isig icanon echo ...) = 0
exit(1)                                 = ?

不成功的一个：

execve("/usr/bin/telnet", ["/usr/bin/telnet", "192.168.0.11", "13"], [/* 22 vars */]) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x4000000, -1, 0) = 0x40005000
stat("/etc/ld.so.cache", st_mode=S_IFREG|0644, st_size=3128, ...) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
mmap2(NULL, 3128, PROT_READ, MAP_SHARED, 3, 0) = 0x40006000
close(3)                                = 0
stat("/etc/ld.so.preload", 0xbe90a8f4)  = -1 ENOENT (No such file or directory)
open("/lib/libc.so.0", O_RDONLY)        = 3
fstat(3, st_mode=S_IFREG|0755, st_size=324423, ...) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x4000000, -1, 0) = 0x40007000
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\320\253\0\0004\0\0\0\0"..., 4096) = 4096
mmap2(NULL, 376832, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4000e000
mmap2(0x4000e000, 319264, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0) = 0x4000e000
mmap2(0x40064000, 4935, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x4e) = 0x40064000
mmap2(0x40066000, 14712, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x40066000
close(3)                                = 0
munmap(0x40007000, 4096)                = 0
munmap(0x40006000, 3128)                = 0
stat("/lib/ld-uClibc.so.0", st_mode=S_IFREG|0755, st_size=20486, ...) = 0
mprotect(0x40064000, 4096, PROT_READ)   = 0
mprotect(0x4000c000, 4096, PROT_READ)   = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbe90a714) = -1 ENOTTY (Inappropriate ioctl for device)
ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbe90a714) = -1 ENOTTY (Inappropriate ioctl for device)
getuid32()                              = 0
ioctl(0, TIOCGWINSZ, 0xbe90a9cc)        = -1 ENOTTY (Inappropriate ioctl for device)
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbe90a9b4) = -1 ENOTTY (Inappropriate ioctl for device)
brk(0)                                  = 0x91000
brk(0x92000)                            = 0x92000
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
connect(3, sa_family=AF_INET, sin_port=htons(13), sin_addr=inet_addr("192.168.0.11"), 16) = 0
setsockopt(3, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
rt_sigaction(SIGINT, 0x667c0, [INT], SA_RESTART|0x4000000, SIG_DFL, [], 0, 8) = 0
poll([fd=0, events=POLLIN, fd=3, events=POLLIN], 2, -1) = 2 ([fd=0, revents=POLLIN, fd=3, revents=POLLIN])
read(0, ""..., 128)                     = 0
exit(0)                                 = ?

欢迎任何帮助。

【参考方案1】：

ioctl(0, TIOCGWINSZ, 0xbe90a9cc)        = -1 ENOTTY (Inappropriate ioctl for device)

我认为这是你的问题。当cron 执行时，您没有相同的环境变量，并且您在常规终端中执行此操作。上一行是两个输出显示的第一个偏差，它看起来像是在设置/检查终端窗口大小（WINSZ），大概是针对telnet 会话窗口。也许检查 cron 脚本中 $TERM 的值？

【参考方案2】：

Ermmm...管道或分离的输入只是不是终端。没有多少环境设置可以解决这个问题。 TRWTF 正在使用来自守护进程的 telnet

简短的故事：使用套接字连接到与您（ab）使用 telnet 的端口相同的端口。这将大大简化您的设置，也不需要终端或子进程

【讨论】：

d'哦，你是完全正确的。我不应该这么早回答问题。