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libstore/ssh: Improve error message on failing execvp

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If the `throw` is reached, this means that execvp into `ssh` wasn’t
successful. We can hint at a usual problem, which is a missing `ssh`
executable.

Test with:

```
env PATH= ./result/bin/nix-copy-closure --builders '' unusedhost
```

and the bash version with

```
env PATH= ./result/bin/nix-copy-closure --builders '' localhost
```

(cherry picked from commit 38b29fb72ca4a07afbec1fd5067f59ca7d7f0fab)
This commit is contained in:
Profpatsch 2019-12-12 15:15:18 +01:00 • committed by Eelco Dolstra
parent 2007b4a89b
commit 7afd8321ed
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GPG key ID: 8170B4726D7198DE
1 changed files with 6 additions and 2 deletions
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8
src/libstore/ssh.cc
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@ -47,10 +47,13 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
throw SysError("duping over stderr"); throw SysError("duping over stderr");
Strings args; Strings args;
const char * execInto;
if (fakeSSH) { if (fakeSSH) {
execInto = "bash";
args = { "bash", "-c" }; args = { "bash", "-c" };
} else { } else {
execInto = "ssh";
args = { "ssh", host.c_str(), "-x", "-a" }; args = { "ssh", host.c_str(), "-x", "-a" };
addCommonSSHOpts(args); addCommonSSHOpts(args);
if (socketPath != "") if (socketPath != "")
@ -62,7 +65,8 @@ std::unique_ptr<SSHMaster::Connection> SSHMaster::startCommand(const std::string
args.push_back(command); args.push_back(command);
execvp(args.begin()->c_str(), stringsToCharPtrs(args).data()); execvp(args.begin()->c_str(), stringsToCharPtrs(args).data());
throw SysError("executing '%s' on '%s'", command, host); // could not exec ssh/bash
throw SysError("Failed to exec into %s. Is it in PATH?", execInto);
}); });
@ -108,7 +112,7 @@ Path SSHMaster::startMaster()
addCommonSSHOpts(args); addCommonSSHOpts(args);
execvp(args.begin()->c_str(), stringsToCharPtrs(args).data()); execvp(args.begin()->c_str(), stringsToCharPtrs(args).data());
throw SysError("starting SSH master"); throw SysError("Failed to exec into ssh. Is it in PATH?");
}); });
out.writeSide = -1; out.writeSide = -1;