调试神秘的git+ssh+proxy失败“bash：没有这样的文件或目录”的艰难方法

Question

调试神秘的git+ssh+proxy失败“bash：没有这样的文件或目录”的艰难方法

我正在尝试通过 SOCKS5 代理克隆 github 存储库。在~/.ssh/config我有：

Host github.com *.github.com
    ProxyCommand /usr/bin/nc -X 5 -x 127.0.0.1:7070 %h %p

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git clone失败并出现错误bash: No such file or directory：

$ git clone git@github.com:aureliojargas/sedsed.git
Cloning into 'sedsed'...
bash: No such file or directory
kex_exchange_identification: Connection closed by remote host
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

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我手动尝试了该ssh命令，但也失败了：

$ ssh -v git@github.com
OpenSSH_8.1p1, LibreSSL 2.7.3
debug1: Reading configuration data /Users/pynexj/.ssh/config
debug1: /Users/pynexj/.ssh/config line 16: Applying options for github.com
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 47: Applying options for *
debug1: Executing proxy command: exec /usr/bin/nc -X 5 -x 127.0.0.1:7070 github.com 22
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
debug1: identity file /Users/pynexj/.ssh/id_rsa type 0
debug1: identity file /Users/pynexj/.ssh/id_rsa-cert type -1
debug1: identity file /Users/pynexj/.ssh/id_dsa type -1
debug1: identity file /Users/pynexj/.ssh/id_dsa-cert type -1
debug1: identity file /Users/pynexj/.ssh/id_ecdsa type -1
debug1: identity file /Users/pynexj/.ssh/id_ecdsa-cert type -1
bash: No such file or directory
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
debug1: identity file /Users/pynexj/.ssh/id_ed25519 type -1
debug1: identity file /Users/pynexj/.ssh/id_ed25519-cert type -1
debug1: identity file /Users/pynexj/.ssh/id_xmss type -1
debug1: identity file /Users/pynexj/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.1
kex_exchange_identification: Connection closed by remote host

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然后我手动尝试了该nc命令，它确实有效：

$ /usr/bin/nc -X 5 -x 127.0.0.1:7070 github.com 22
SSH-2.0-babeld-8cd15329
^C

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SOCKS5 代理也可以正常工作：

$ ssh -v git@github.com
OpenSSH_8.1p1, LibreSSL 2.7.3
debug1: Reading configuration data /Users/pynexj/.ssh/config
debug1: /Users/pynexj/.ssh/config line 16: Applying options for github.com
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 47: Applying options for *
debug1: Executing proxy command: exec /usr/bin/nc -X 5 -x 127.0.0.1:7070 github.com 22
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
debug1: identity file /Users/pynexj/.ssh/id_rsa type 0
debug1: identity file /Users/pynexj/.ssh/id_rsa-cert type -1
debug1: identity file /Users/pynexj/.ssh/id_dsa type -1
debug1: identity file /Users/pynexj/.ssh/id_dsa-cert type -1
debug1: identity file /Users/pynexj/.ssh/id_ecdsa type -1
debug1: identity file /Users/pynexj/.ssh/id_ecdsa-cert type -1
bash: No such file or directory
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
debug1: identity file /Users/pynexj/.ssh/id_ed25519 type -1
debug1: identity file /Users/pynexj/.ssh/id_ed25519-cert type -1
debug1: identity file /Users/pynexj/.ssh/id_xmss type -1
debug1: identity file /Users/pynexj/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.1
kex_exchange_identification: Connection closed by remote host

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我很好奇谁（以及为什么）产生了错误bash: no such file or directory。

Answer 1

pyn*_*exj 5

对我来说，这个问题是 macOS 特有的。我在 Google 上搜索了很多，发现 macOS 10.15 (Catalina) 上有许多损坏的 SSH 案例，但没有一个解决方法对我有用。最终我不得不查看 OpenSSH 代码并发现了问题。

在源文件sshconnect.c中：

 194 static int
 195 ssh_proxy_connect(struct ssh *ssh, const char *host, const char *host_arg,
 196     u_short port, const char *proxy_command)
 197 {
 ...
 ...
 201     char *shell;
 202
 203     if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
 204         shell = _PATH_BSHELL;
 ...
 ...
 211     command_string = expand_proxy_command(proxy_command, options.user,
 212         host, host_arg, port);
 213     debug("Executing proxy command: %.500s", command_string);
 214
 215     /* Fork and execute the proxy command. */
 216     if ((pid = fork()) == 0) {
 217         char *argv[10];
 ...
 ...
 240         argv[0] = shell;
 241         argv[1] = "-c";
 242         argv[2] = command_string;
 243         argv[3] = NULL;
 244
 245         /* Execute the proxy command.  Note that we gave up any
 246            extra privileges above. */
 247         ssh_signal(SIGPIPE, SIG_DFL);
 248         execv(argv[0], argv);
 249         perror(argv[0]);
 250         exit(1);
 251     }

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请参阅第 203、240 和 248 行，ssh 正在尝试使用 ProxyCommand 运行（我$SHELL ^{没有找到这方面的文档）}，并且它使用execv()，它不会在$PATH. 然后我检查了我的$SHELL：

$ echo $SHELL
bash

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这就是问题所在。$SHELL不是完整路径名可执行文件，因此execv()无法执行它，错误bash: No such file or directory来自第 249 行中的perror() ^{。（这个错误让我很困惑。前缀bash:让我认为错误来自 Bash。）}

解决方案：手动设置SHELL为 shell 的完整路径名，例如/bin/bash. ^{（我没有写shell /bin/bash，.screenrc因为我也有/usr/local/bin/bash。）}

那么谁定呢SHELL=bash？为什么不设定SHELL=/bin/bash？

在我的~/.screenrc我有：

shell bash

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根据屏幕手册：

外壳命令

设置用于创建新 shell 的命令。 这会覆盖环境变量的值$SHELL。

在我启动 screen 之前， varSHELL最初/bin/bash位于我的交互式 shell 中，因此是 screen 设置的SHELL=bash。我认为 screen 应该找出 shell 的完整路径名并设置SHELL为完整路径名，因为根据posix：

该变量应表示用户首选命令语言解释器的路径名。

那么为什么它在我的 Linux 系统（Debian）上运行得很好SHELL=bash（也在屏幕上）？

我做了一个strace并得到了这个：

$ SHELL=xxx strace -f ssh git@github.com
[...]
[pid  5767] rt_sigaction(SIGPIPE, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
[pid  5767] execve("/root/bin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] execve("/usr/local/bin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] execve("/usr/local/sbin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] execve("/usr/sbin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] execve("/usr/bin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] execve("/sbin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] execve("/bin/xxx", ["xxx", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x561e33a599a0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid  5767] dup(2)                      = 3
[pid  5767] fcntl(3, F_GETFL)           = 0x8402 (flags O_RDWR|O_APPEND|O_LARGEFILE)
[pid  5767] fstat(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x21), ...}) = 0
[pid  5767] write(3, "xxx: No such file or directory\n", 31xxx: No such file or directory
) = 31
[pid  5767] close(3)                    = 0
[...]

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正如我们所看到的，它实际上是xxx在中搜索$PATH。为什么？我想 Debian 一定已经修补了 openssh 并改变了它的行为。^{（如果我知道 Debian 构建内部结构，我会验证这一点。:-)}

2020年11月19日更新：

我从源代码手动编译了 OpenSSH (v8.4) ，并在 Debian 上重现了相同的问题。这证实 Debian 已经修补了 OpenSSH 并改变了其行为。

$ /usr/local/openssh-8.4/bin/ssh git@github.com
bash: No such file or directory
kex_exchange_identification: Connection closed by remote host
$ strace -f /usr/local/openssh-8.4/bin/ssh git@github.com
[...]
[pid 21020] rt_sigaction(SIGPIPE, {sa_handler=SIG_DFL, sa_mask=~[RTMIN RT_1], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f19a05a9840}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
[pid 21020] execve("bash", ["bash", "-c", "exec nc -X 5 -x 127.0.0.1:7070 g"...], 0x5566982872f0 /* 33 vars */) = -1 ENOENT (No such file or directory)
[pid 21020] dup(2)                      = 3
[pid 21020] fcntl(3, F_GETFL)           = 0x8402 (flags O_RDWR|O_APPEND|O_LARGEFILE)
[pid 21020] fstat(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x25), ...}) = 0
[pid 21020] write(3, "bash: No such file or directory\n", 32bash: No such file or directory
) = 32
[pid 21020] close(3)
[...]

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