[email protected] (Kenny McCormack) writes:

When I do: ls -lsa /proc/<pid>/fd
I often see fds open on pipes, and the notation is like:

3 -> pipe:[123456]

where 123456 is a sequence of usually between 6 and 8 digits. My question >is: To what does this number map? What does it mean?

First guess, the pid of the process on the other side of the pipe (which
may be the same process or a child process).

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When I do: ls -lsa /proc/<pid>/fd
I often see fds open on pipes, and the notation is like:

3 -> pipe:[123456]

where 123456 is a sequence of usually between 6 and 8 digits. My question
is: To what does this number map? What does it mean?

Almost certainly, there is something else in /proc that contains this
number and identifies the pipe in use. Usually, I'm pretty good about
sussing things like this out - usually the answer is in "man /proc", but
this one has me stumped.

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us the most embarrassed by it.

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[email protected] (Scott Lurndal) writes:

[email protected] (Kenny McCormack) writes:

When I do: ls -lsa /proc/<pid>/fd
I often see fds open on pipes, and the notation is like:

3 -> pipe:[123456]

where 123456 is a sequence of usually between 6 and 8 digits. My question >>is: To what does this number map? What does it mean?

First guess, the pid of the process on the other side of the pipe (which
may be the same process or a child process).

It's the inode number of the pipe.

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In article <[email protected]>, Ralf Fassel <[email protected]> wrote: ...

type:[inode]

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to
find more information in one of the files under
/proc/net/.

HTH

It pretty much tells me things I already knew.

What I'm looking for is "What can I do with this number?" You say it is an "inode" number, but I doubt it is matches to a file in the file system.
I.e., you would do: find / -inum 123456 -ls

Longer term, what I am really looking for is "Who is on the other end of
this pipe?"

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* [email protected] (Kenny McCormack)
| When I do: ls -lsa /proc/<pid>/fd
| I often see fds open on pipes, and the notation is like:

| 3 -> pipe:[123456]

| where 123456 is a sequence of usually between 6 and 8 digits. My
| question is: To what does this number map? What does it mean?

https://man7.org/linux/man-pages/man5/proc.5.html
[...]
/proc/[pid]/fd/
This is a subdirectory containing one entry for each file
which the process has open, named by its file descriptor,
and which is a symbolic link to the actual file. Thus, 0
is standard input, 1 standard output, 2 standard error,
and so on.

For file descriptors for pipes and sockets, the entries
will be symbolic links whose content is the file type with
the inode. A readlink(2) call on this file returns a
string in the format:

type:[inode]

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to
find more information in one of the files under
/proc/net/.

HTH
R'

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[email protected] (Kenny McCormack) writes:

In article <[email protected]>, Ralf Fassel <[email protected]> wrote: ...

type:[inode]

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to
find more information in one of the files under
/proc/net/.

HTH

It pretty much tells me things I already knew.

What I'm looking for is "What can I do with this number?" You say it is an "inode" number, but I doubt it is matches to a file in the file system.
I.e., you would do: find / -inum 123456 -ls

Longer term, what I am really looking for is "Who is on the other end of
this pipe?"

Assuming you know the inode number, lsof | grep <inode number> will tell
you that (ls -l /prroc/*/fd | grep ...).

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Scott Lurndal, dans le message <9xK0J.78844$[email protected]>, a
�crit�:

First guess, the pid of the process on the other side of the pipe

There is absolutely no chance of that, since several processes can have the same file descriptor.

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* [email protected] (Kenny McCormack)
| Longer term, what I am really looking for is "Who is on the other end
| of this pipe?"

I just did a

$ cat | cat

$ ps -ef | grep cat
UID PID PPID C STIME TTY TIME CMD
user 28788 28758 0 10:42 pts/4 00:00:00 cat
user 28789 28758 0 10:42 pts/4 00:00:00 cat

$ ls -l /proc/28788/fd
l-wx------ 1 user group 64 Sep 17 10:42 1 -> pipe:[6418237]

$ ls -l /proc/28789/fd
lr-x------ 1 user group 64 Sep 17 10:42 0 -> pipe:[6418237]

While there seems to be no file on /proc with that inode:

$ find /proc -inum 6418237 2>/dev/null
[nada]

you could ls -l /proc/*/fd and check for the same inode listed in the
last field. Don't know how bullet-proof this is...

R'

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with <shvvnv$2667d$[email protected]> Kenny McCormack wrote:

In article <[email protected]>, Ralf Fassel <[email protected]> wrote:

type:[inode]

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to
find more information in one of the files under
/proc/net/.

HTH

It pretty much tells me things I already knew.

What I'm looking for is "What can I do with this number?" You say it
is an "inode" number, but I doubt it is matches to a file in the file
system. I.e., you would do: find / -inum 123456 -ls

Longer term, what I am really looking for is "Who is on the other end
of this pipe?"

If it's listening, then probably nothing. Anyway, quick grep through
'man lsof' suggests '/proc/net/unix'.

--
Torvalds' goal for Linux is very simple: World Domination
Stallman's goal for GNU is even simpler: Freedom

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Eric Pozharski <[email protected]> writes:

with <shvvnv$2667d$[email protected]> Kenny McCormack wrote:

In article <[email protected]>, Ralf Fassel <[email protected]> wrote:

type:[inode]

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to
find more information in one of the files under
/proc/net/.

HTH

It pretty much tells me things I already knew.

What I'm looking for is "What can I do with this number?" You say it
is an "inode" number, but I doubt it is matches to a file in the file
system. I.e., you would do: find / -inum 123456 -ls

Longer term, what I am really looking for is "Who is on the other end
of this pipe?"

If it's listening, then probably nothing. Anyway, quick grep through
'man lsof' suggests '/proc/net/unix'.

A pipe is not a UNIX domain socket (listed in /proc/net/unix).

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On Thu, 16 Sep 2021 17:43:27 +0000, Kenny McCormack wrote:

In article <[email protected]>, Ralf Fassel <[email protected]> wrote: ...

type:[inode]

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to
find more information in one of the files under
/proc/net/.

HTH

It pretty much tells me things I already knew.

What I'm looking for is "What can I do with this number?" You say it is an "inode" number, but I doubt it is matches to a file in the file system.
I.e., you would do: find / -inum 123456 -ls

Longer term, what I am really looking for is "Who is on the other end of
this pipe?"

Sorry, but I don't think you will be able to answer that question directly.

Apparently, from reading /usr/src/linux/fs/pipe.c, Linux implements pipes within a pseudo-filesystem called "pipefs". Those inode numbers refer to
inodes within this pseudo-filesystem.

According to Linux.org (among others),
"Pipefs is a unique virtual filesystem. This filesystem is mounted
inside the kernel rather than in the userspace. While most filesystems
are mounted under "/", PipeFS is mounted on "pipe:", making PipeFS its
own root (yes, a second root filesystem). This filesystem is one
superblock and cannot exceed that amount system-wide. The entry point
of this filesystem/second-root is the system-call "pipe()". Unlike
the other virtual/pseudo filesystems, this one cannot be viewed." (https://www.linux.org/threads/pipefs-sockfs-debugfs-and-securityfs.9638/)

So, those pipe inode numbers address inodes in a filesystem that is not externalized to /any/ subtree of /. This makes it difficult to use userland utilities (like find, for instance) on the pipefs, and thus makes analysis
of individual pipe pairs /very/ difficult.

IDK, but you /might/ be able to explicitly mount pipefs to some part of the filesystem tree. I can't guarantee that this will work, nor can I speculate
on /if/ any userland utility would be able to access it to provide you with
the information you seek.

HTH
--
Lew Pitcher
"In Skills, We Trust"

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with <[email protected]> Rainer
Weikusat wrote:

Eric Pozharski <[email protected]> writes:

with <shvvnv$2667d$[email protected]> Kenny McCormack wrote:

In article <[email protected]>, Ralf Fassel
<[email protected]> wrote:

*SKIP*

For example, socket:[2248868] will be a socket and its
inode is 2248868. For sockets, that inode can be used to >>>> find more information in one of the files under
/proc/net/.

It pretty much tells me things I already knew.
What I'm looking for is "What can I do with this number?" You say
it is an "inode" number, but I doubt it is matches to a file in the
file system. I.e., you would do: find / -inum 123456 -ls
Longer term, what I am really looking for is "Who is on the other
end of this pipe?"

If it's listening, then probably nothing. Anyway, quick grep through
'man lsof' suggests '/proc/net/unix'.

A pipe is not a UNIX domain socket (listed in /proc/net/unix).

Indeed (as you can see, pipes quickly diverted to sockets as easier
targets). As pointed out in <si2qip$8e1$[email protected]> pipes don't
manifest in something like /proc/net/unix. Scanning through
/proc/[0-9]*/fd/* then.

--
Torvalds' goal for Linux is very simple: World Domination
Stallman's goal for GNU is even simpler: Freedom

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In article <[email protected]>,
Rainer Weikusat <[email protected]> wrote:
...

Longer term, what I am really looking for is "Who is on the other end of
this pipe?"

Assuming you know the inode number, lsof | grep <inode number> will tell
you that (ls -l /prroc/*/fd | grep ...).

Yeah, it may come to that.

But I was hoping for more of a "metal detector" type solution, rather than searching the entire haystack looking for the needle. I.e., more of a "go here" answer, than a "polling" answer.

But, thanks...

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laws, and more police authority to make warrantless arrests to remind
us that we need to "get the government off our backs".

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In article <si2qip$8e1$[email protected]>,
Lew Pitcher <[email protected]> wrote:
...

Sorry, but I don't think you will be able to answer that question directly.

Yeah, that's kinda what I feared.

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In article <si2qip$8e1$[email protected]>,
Lew Pitcher <[email protected]> wrote:
...

IDK, but you /might/ be able to explicitly mount pipefs to some part of the >filesystem tree. I can't guarantee that this will work, nor can I speculate >on /if/ any userland utility would be able to access it to provide you with >the information you seek.

# mkdir /tmp/ook
# mount -t pipefs none /tmp/ook
mount: /tmp/ook: wrong fs type, bad option, bad superblock on none, missing codepage or helper program, or other error.
# mount -t pipes none /tmp/ook
mount: /tmp/ook: unknown filesystem type 'pipes'.
# mount -t proc none /tmp/ook
#

--
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community college.
- F. Russell -

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