Which Unix-like system really provides the /dev/tcp special file?

I know /dev/tcp/<host>/<port> is a magic path handled specifically by some shells in redirections. But according to man bash:

If the operating system on which bash is running provides these special files, bash will use them; otherwise it will emulate them internally
[...]

On the Linux box I am using right now, the /dev/tcp special file is not present, so the Bash will emulate it. But, is there actually a Unix-like system that does provide the /dev/tcp special file with the same semantic as the one supported by the Bash?

asked Jan 14 at 11:25

Sylvain Leroux

478212

It would require an emulated directory. Making emulated directories is possible only with specific filesystems, for example procfs or sysfs can do that. /dev is a tmpfs on current linuxes, and it was on the root partition in older ones. This is why it is impossible currently. It could be made possible easily with a sysfs or procfs extension (both fs are very flexible and similar (actually probably no one knows why they aren't the same)), no one does it today, but it could be made in around 100 lines of code.

– peterh
Jan 14 at 11:58

But is there any other OS that does it already? At some point, I thought Plan 9 did it but I was wrong.

– Sylvain Leroux
Jan 14 at 12:42

1

I don't know, probably not (as far I know, it is a bash invention). I voted your question up, because the answer is interesting also to me. As far I know, no popular x86-capable unix OS can do this.

– peterh
Jan 14 at 12:44

add a comment |

I know /dev/tcp/<host>/<port> is a magic path handled specifically by some shells in redirections. But according to man bash:

If the operating system on which bash is running provides these special files, bash will use them; otherwise it will emulate them internally
[...]

asked Jan 14 at 11:25

Sylvain Leroux

478212

It would require an emulated directory. Making emulated directories is possible only with specific filesystems, for example procfs or sysfs can do that. /dev is a tmpfs on current linuxes, and it was on the root partition in older ones. This is why it is impossible currently. It could be made possible easily with a sysfs or procfs extension (both fs are very flexible and similar (actually probably no one knows why they aren't the same)), no one does it today, but it could be made in around 100 lines of code.

– peterh
Jan 14 at 11:58

But is there any other OS that does it already? At some point, I thought Plan 9 did it but I was wrong.

– Sylvain Leroux
Jan 14 at 12:42

1

I don't know, probably not (as far I know, it is a bash invention). I voted your question up, because the answer is interesting also to me. As far I know, no popular x86-capable unix OS can do this.

– peterh
Jan 14 at 12:44

add a comment |

I know /dev/tcp/<host>/<port> is a magic path handled specifically by some shells in redirections. But according to man bash:

If the operating system on which bash is running provides these special files, bash will use them; otherwise it will emulate them internally
[...]

asked Jan 14 at 11:25

Sylvain Leroux

478212

I know /dev/tcp/<host>/<port> is a magic path handled specifically by some shells in redirections. But according to man bash:

If the operating system on which bash is running provides these special files, bash will use them; otherwise it will emulate them internally
[...]

devices tcp character-special-files

asked Jan 14 at 11:25

Sylvain Leroux

478212

asked Jan 14 at 11:25

Sylvain Leroux

478212

asked Jan 14 at 11:25

Sylvain Leroux

478212

asked Jan 14 at 11:25

Sylvain Leroux

478212

asked Jan 14 at 11:25

Sylvain Leroux

478212

It would require an emulated directory. Making emulated directories is possible only with specific filesystems, for example procfs or sysfs can do that. /dev is a tmpfs on current linuxes, and it was on the root partition in older ones. This is why it is impossible currently. It could be made possible easily with a sysfs or procfs extension (both fs are very flexible and similar (actually probably no one knows why they aren't the same)), no one does it today, but it could be made in around 100 lines of code.

– peterh
Jan 14 at 11:58

But is there any other OS that does it already? At some point, I thought Plan 9 did it but I was wrong.

– Sylvain Leroux
Jan 14 at 12:42

1

I don't know, probably not (as far I know, it is a bash invention). I voted your question up, because the answer is interesting also to me. As far I know, no popular x86-capable unix OS can do this.

– peterh
Jan 14 at 12:44

add a comment |

It would require an emulated directory. Making emulated directories is possible only with specific filesystems, for example procfs or sysfs can do that. /dev is a tmpfs on current linuxes, and it was on the root partition in older ones. This is why it is impossible currently. It could be made possible easily with a sysfs or procfs extension (both fs are very flexible and similar (actually probably no one knows why they aren't the same)), no one does it today, but it could be made in around 100 lines of code.

– peterh
Jan 14 at 11:58

But is there any other OS that does it already? At some point, I thought Plan 9 did it but I was wrong.

– Sylvain Leroux
Jan 14 at 12:42

1

I don't know, probably not (as far I know, it is a bash invention). I voted your question up, because the answer is interesting also to me. As far I know, no popular x86-capable unix OS can do this.

– peterh
Jan 14 at 12:44

It would require an emulated directory. Making emulated directories is possible only with specific filesystems, for example procfs or sysfs can do that. /dev is a tmpfs on current linuxes, and it was on the root partition in older ones. This is why it is impossible currently. It could be made possible easily with a sysfs or procfs extension (both fs are very flexible and similar (actually probably no one knows why they aren't the same)), no one does it today, but it could be made in around 100 lines of code.

– peterh
Jan 14 at 11:58

But is there any other OS that does it already? At some point, I thought Plan 9 did it but I was wrong.

– Sylvain Leroux
Jan 14 at 12:42

I don't know, probably not (as far I know, it is a bash invention). I voted your question up, because the answer is interesting also to me. As far I know, no popular x86-capable unix OS can do this.

– peterh
Jan 14 at 12:44

add a comment |

1 Answer
1

active

oldest

votes

I think the Bash documentation is somewhat misleading on this topic. Looking at the code, even going back to version 2.04 where network redirections were introduced, /dev/tcp and /dev/udp works as follows:

at build time, the configure script checks to see whether various networking features are supported; if so, if network redirections are enabled (which is the case by default), internal networking code is built in;

at run time, if the internal networking code is built in, /dev/tcp and /dev/udp (in the right format) are handled internally; otherwise, a warning is produced (“/dev/(tcp|udp)/host/port not supported without networking”) and Bash attempts to open the given path on the system;

if network redirections are configured out, nothing special is done.

What this boils down to is:

if network redirection is enabled:
- if networking is supported on the target platform, /dev/tcp and /dev/udp will always be handled internally;
- otherwise, Bash will warn and try to open the file “blindly”; if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail;

if network redirection is disabled, no special handling is performed; as above, if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail.

/dev/tcp does exist on some systems, but as far as I’m aware none support the same abstraction as Bash. On Solaris, /dev/tcp is used with the ndd tool to query and change network configuration. In XTI (see also the Open Group if you’re a member), the t_open function can be used with /dev/tcp to open a TCP connection, but it doesn’t use path-based setup, there’s a separate data structure to specify the target host and port (and other parameters).

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

The feature itself comes from ksh93. /dev/tcp on SysV systems would be a handle on the STREAMS tcp module.

– Stéphane Chazelas
Jan 14 at 17:00

add a comment |

Your Answer

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "106"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f494389%2fwhich-unix-like-system-really-provides-the-dev-tcp-special-file%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

at build time, the configure script checks to see whether various networking features are supported; if so, if network redirections are enabled (which is the case by default), internal networking code is built in;

at run time, if the internal networking code is built in, /dev/tcp and /dev/udp (in the right format) are handled internally; otherwise, a warning is produced (“/dev/(tcp|udp)/host/port not supported without networking”) and Bash attempts to open the given path on the system;

if network redirections are configured out, nothing special is done.

What this boils down to is:

if network redirection is enabled:
- if networking is supported on the target platform, /dev/tcp and /dev/udp will always be handled internally;
- otherwise, Bash will warn and try to open the file “blindly”; if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail;

if network redirection is disabled, no special handling is performed; as above, if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail.

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

The feature itself comes from ksh93. /dev/tcp on SysV systems would be a handle on the STREAMS tcp module.

– Stéphane Chazelas
Jan 14 at 17:00

add a comment |

at build time, the configure script checks to see whether various networking features are supported; if so, if network redirections are enabled (which is the case by default), internal networking code is built in;

at run time, if the internal networking code is built in, /dev/tcp and /dev/udp (in the right format) are handled internally; otherwise, a warning is produced (“/dev/(tcp|udp)/host/port not supported without networking”) and Bash attempts to open the given path on the system;

if network redirections are configured out, nothing special is done.

What this boils down to is:

if network redirection is enabled:
- if networking is supported on the target platform, /dev/tcp and /dev/udp will always be handled internally;
- otherwise, Bash will warn and try to open the file “blindly”; if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail;

if network redirection is disabled, no special handling is performed; as above, if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail.

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

The feature itself comes from ksh93. /dev/tcp on SysV systems would be a handle on the STREAMS tcp module.

– Stéphane Chazelas
Jan 14 at 17:00

add a comment |

at build time, the configure script checks to see whether various networking features are supported; if so, if network redirections are enabled (which is the case by default), internal networking code is built in;

at run time, if the internal networking code is built in, /dev/tcp and /dev/udp (in the right format) are handled internally; otherwise, a warning is produced (“/dev/(tcp|udp)/host/port not supported without networking”) and Bash attempts to open the given path on the system;

if network redirections are configured out, nothing special is done.

What this boils down to is:

if network redirection is enabled:
- if networking is supported on the target platform, /dev/tcp and /dev/udp will always be handled internally;
- otherwise, Bash will warn and try to open the file “blindly”; if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail;

if network redirection is disabled, no special handling is performed; as above, if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail.

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

at build time, the configure script checks to see whether various networking features are supported; if so, if network redirections are enabled (which is the case by default), internal networking code is built in;

at run time, if the internal networking code is built in, /dev/tcp and /dev/udp (in the right format) are handled internally; otherwise, a warning is produced (“/dev/(tcp|udp)/host/port not supported without networking”) and Bash attempts to open the given path on the system;

if network redirections are configured out, nothing special is done.

What this boils down to is:

if network redirection is enabled:
- if networking is supported on the target platform, /dev/tcp and /dev/udp will always be handled internally;
- otherwise, Bash will warn and try to open the file “blindly”; if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail;

if network redirection is disabled, no special handling is performed; as above, if the system somehow supports /dev/(tcp|udp)/host/port, that will be used, otherwise in all likelihood the redirection will fail.

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

answered Jan 14 at 13:27

Stephen Kitt

172k24386464

The feature itself comes from ksh93. /dev/tcp on SysV systems would be a handle on the STREAMS tcp module.

– Stéphane Chazelas
Jan 14 at 17:00

add a comment |

The feature itself comes from ksh93. /dev/tcp on SysV systems would be a handle on the STREAMS tcp module.

– Stéphane Chazelas
Jan 14 at 17:00

The feature itself comes from ksh93. /dev/tcp on SysV systems would be a handle on the STREAMS tcp module.

– Stéphane Chazelas
Jan 14 at 17:00

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Unix & Linux Stack Exchange!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

Search This Blog

Ufyukyu