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ramu
*nix forums beginner
Joined: 13 Jan 2006
Posts: 25
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 Posted: Fri Jun 09, 2006 10:04 am Post subject:
difference between normal file and named pipe file
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HI,
will anyone let me know the differences between the normal unix
file and named pipe file?
Regards |
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Barry Margolin
*nix forums Guru
Joined: 24 Feb 2005
Posts: 323
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| Posted: Fri Jun 09, 2006 1:02 pm Post subject:
Re: difference between normal file and named pipe file
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In article <1149847461.686160.120590@j55g2000cwa.googlegroups.com>,
"ramu" <ramu.ask@gmail.com> wrote:
| Quote: | HI,
will anyone let me know the differences between the normal unix
file and named pipe file?
|
A normal file is a bunch of data sitting on disk.
A named pipe is a way for two processes to connect to each other and
send data directly.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group *** |
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colonel_hack@yahoo.com
*nix forums beginner
Joined: 26 Jul 2005
Posts: 5
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| Posted: Fri Jun 09, 2006 3:28 pm Post subject:
Re: difference between normal file and named pipe file
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| Quote: | In article <1149847461.686160.120590@j55g2000cwa.googlegroups.com>,
"ramu" <ramu.ask@gmail.com> wrote:
HI,
will anyone let me know the differences between the normal unix
file and named pipe file?
|
A file keeps all the data until deleted/overwritten while iiuc a named
pipe dumps the data after it is read. So a temp file could keep growing
and fill a file system, but a named pipe is less likey to for, say, long
running processes.
3ch |
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Andrew Smallshaw
*nix forums beginner
Joined: 23 Feb 2005
Posts: 26
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| Posted: Mon Jun 12, 2006 4:44 pm Post subject:
Re: difference between normal file and named pipe file
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On 2006-06-09, colonel_hack@yahoo.com <colonel_hack@yahoo.com> wrote:
| Quote: |
A file keeps all the data until deleted/overwritten while iiuc a named
pipe dumps the data after it is read. So a temp file could keep growing
and fill a file system, but a named pipe is less likey to for, say, long
running processes.
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I'm not sure I understand this - a write to a named pipe will block if
there is no corresponding process reading from the pipe, usually
blocking the whole process until there's a reader. This in itself is
can be quite a useful shell hack - it allows to send a signal between
two processes, potentially owned by different users, without root
permissions being needed.
--
Andrew Smallshaw
andrews@sdf.lonestar.org |
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colonel_hack@yahoo.com
*nix forums beginner
Joined: 26 Jul 2005
Posts: 5
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| Posted: Tue Jun 13, 2006 9:41 pm Post subject:
Re: difference between normal file and named pipe file
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~On Mon, 12 Jun 2006, Andrew Smallshaw wrote:
| Quote: | On 2006-06-09, colonel_hack@yahoo.com <colonel_hack@yahoo.com> wrote:
A file keeps all the data until deleted/overwritten while iiuc a named
pipe dumps the data after it is read. So a temp file could keep growing
and fill a file system, but a named pipe is less likey to for, say, long
running processes.
I'm not sure I understand this - a write to a named pipe will block if
there is no corresponding process reading from the pipe, usually
blocking the whole process until there's a reader. This in itself is
can be quite a useful shell hack - it allows to send a signal between
two processes, potentially owned by different users, without root
permissions being needed.
|
I'm not sure what part you don't understand (perhaps I've said something
wrong) but:
An open for writing to a named pipe will block if there is no process with
the file open for reading (and vice versa). But it dosen't have to be
actively reading for the writer to write, so the file can still grow. I
think there is also some smaller limit that for a normal file. But the
blocking scheme is also an important difference.
3ch |
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Barry Margolin
*nix forums Guru
Joined: 24 Feb 2005
Posts: 323
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| Posted: Wed Jun 14, 2006 4:06 am Post subject:
Re: difference between normal file and named pipe file
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In article <20060613083148.E733@nonsuch.ronnet.moc>,
colonel_hack@yahoo.com wrote:
| Quote: | ~On Mon, 12 Jun 2006, Andrew Smallshaw wrote:
On 2006-06-09, colonel_hack@yahoo.com <colonel_hack@yahoo.com> wrote:
A file keeps all the data until deleted/overwritten while iiuc a named
pipe dumps the data after it is read. So a temp file could keep growing
and fill a file system, but a named pipe is less likey to for, say, long
running processes.
I'm not sure I understand this - a write to a named pipe will block if
there is no corresponding process reading from the pipe, usually
blocking the whole process until there's a reader. This in itself is
can be quite a useful shell hack - it allows to send a signal between
two processes, potentially owned by different users, without root
permissions being needed.
I'm not sure what part you don't understand (perhaps I've said something
wrong) but:
An open for writing to a named pipe will block if there is no process with
the file open for reading (and vice versa). But it dosen't have to be
actively reading for the writer to write, so the file can still grow.
|
What file? There's no file associated with a named pipe, it's just a
kernel connection between the two processes.
| Quote: | I
think there is also some smaller limit that for a normal file. But the
blocking scheme is also an important difference.
|
There's typically a buffer of about 4KB in the kernel. So if the writer
writes faster than the reader reads, the writer will block when it gets
4K ahead of the reader.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group *** |
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ramu
*nix forums beginner
Joined: 13 Jan 2006
Posts: 25
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| Posted: Wed Jun 14, 2006 7:46 am Post subject:
Re: difference between normal file and named pipe file
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Well. Thanks for your answers. The differences what you have given are
functional. Can anyone tell me the implementation level differencs
between normal unix files and named pipe files?
Regards |
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colonel_hack@yahoo.com
*nix forums beginner
Joined: 26 Jul 2005
Posts: 5
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| Posted: Wed Jun 14, 2006 4:30 pm Post subject:
Re: difference between normal file and named pipe file
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On Wed, 14 Jun 2006, Barry Margolin wrote:
| Quote: | What file? There's no file associated with a named pipe, it's just a
kernel connection between the two processes.
A -named- pipe? Per Maurice Bach in The Design of the Unix operating |
system: "A named pipe is a file whose semantics are the same as those of
an unnamed pipe, except it has a directory entry and is accessed by a path
name." Also he says the size limit is set by the use of only direct blocks
of the inode but he is talking about System V
Under FreeBSD (and similar under Fedora core 3):
%ls
%
%mkfifo joe
%ls
joe
%echo "1234567890" > joe
hangs until I do
%cat joe
1234567890
%
in another terminal.
and
%ls -i
147374 joe
show it has an inode
| Quote: | There's typically a buffer of about 4KB in the kernel. So if the writer
writes faster than the reader reads, the writer will block when it gets
4K ahead of the reader.
Perhaps in modern unices the name is stored in the file system but data |
in buffers, but it has a directory entry and and inode. That is what I
meant by calling it a file anyway.
This has encouraged me read up on named pipes though :-)
3ch |
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Barry Margolin
*nix forums Guru
Joined: 24 Feb 2005
Posts: 323
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| Posted: Thu Jun 15, 2006 12:04 am Post subject:
Re: difference between normal file and named pipe file
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In article <20060614084958.A81933@nonsuch.ronnet.moc>,
colonel_hack@yahoo.com wrote:
| Quote: | On Wed, 14 Jun 2006, Barry Margolin wrote:
What file? There's no file associated with a named pipe, it's just a
kernel connection between the two processes.
A -named- pipe? Per Maurice Bach in The Design of the Unix operating
system: "A named pipe is a file whose semantics are the same as those of
an unnamed pipe, except it has a directory entry and is accessed by a path
name." Also he says the size limit is set by the use of only direct blocks
of the inode but he is talking about System V
Under FreeBSD (and similar under Fedora core 3):
%ls
%
%mkfifo joe
%ls
joe
%echo "1234567890" > joe
hangs until I do
%cat joe
1234567890
%
in another terminal.
and
%ls -i
147374 joe
show it has an inode
There's typically a buffer of about 4KB in the kernel. So if the writer
writes faster than the reader reads, the writer will block when it gets
4K ahead of the reader.
Perhaps in modern unices the name is stored in the file system but data
in buffers, but it has a directory entry and and inode. That is what I
meant by calling it a file anyway.
|
If everything that has a directory entry is a file, then yes it's a
file, and so is a tty device, tape drive, etc. I was using the term in
the more traditional sense to mean a collection of non-volatile data on
some storage medium.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group *** |
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colonel_hack@yahoo.com
*nix forums beginner
Joined: 26 Jul 2005
Posts: 5
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| Posted: Thu Jun 15, 2006 4:46 am Post subject:
Re: difference between normal file and named pipe file
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On Wed, 14 Jun 2006, Barry Margolin wrote:
| Quote: |
If everything that has a directory entry is a file, then yes it's a
file, and so is a tty device, tape drive, etc. I was using the term in
the more traditional sense to mean a collection of non-volatile data on
some storage medium.
|
More traditional outside of unix, but it is the standard unix terminology.
"Everything is a file" and all that.
3ch |
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Barry Margolin
*nix forums Guru
Joined: 24 Feb 2005
Posts: 323
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| Posted: Thu Jun 15, 2006 12:51 pm Post subject:
Re: difference between normal file and named pipe file
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In article <20060614163845.R7173@nonsuch.ronnet.moc>,
colonel_hack@yahoo.com wrote:
| Quote: | On Wed, 14 Jun 2006, Barry Margolin wrote:
If everything that has a directory entry is a file, then yes it's a
file, and so is a tty device, tape drive, etc. I was using the term in
the more traditional sense to mean a collection of non-volatile data on
some storage medium.
More traditional outside of unix, but it is the standard unix terminology.
"Everything is a file" and all that.
|
Yeah, I never was a big fan of Unix's term "special file".
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group *** |
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