UNIX for Dummies Questions & Answers

Hello All,

Friends i know mknod with -p option is used to create FIFO special file.

But i want to know some circumstance/scenario where these are used.

Actually i want to know where i can use it in real time.

Please advise.

actually, it has no -p option. it has a p type, like

Code:

mknod fifo-file p

where can you use it in real time? any UNIX system.

What are they used for? Bridging together programs which are difficult to use anonymous pipes with. To get an anonymous pipe you have to be a child process of whatever created it, but named pipes can be opened by any arbitrary process, child or not.

They're also used to make dynamic things which act like files, so when something tries to read what used to be a config file or somesuch they get dynamically-generated output from a program.

As an addendum to Corona's words of wisdom:
Look up what the letters in "fifo" traditionally stand for, if you don't already know.

If you want to see a simple real-world example, check out a little script I created for someone recently: https://github.com/ryran/b19scripts/...er/net-notifyd

Well, I use them for database backups/exports, e.g. for Oracle:-

Code:

$ cat robin.par
USERID=system
        FILE=/robin/robin.dat
        LOG=/robin/robin.explog
        OWNER=robin
$ mknod /robin/robin.dat p
$ dd if=/robin/robin.dat | compress > =/robin/robin.dat.Z &
$ exp parfile=robin.par

I have also used it for service automation where a privileged and sensitive procedure needs to be demanded by other users. I wrote a script to loop on something being written to a pipe and then it would perform the action. I was very careful to make sure that the "do this" message was strictly checked because it was a bit sensitive, but then I could open the pipe file to be written by an appropriate group of people. It saved me no end of overnight calls.

They are very useful, but getting some good examples as to when to use them is difficult. If you can create a chain of commands using pipes to perform an operation then you could do it through pipe files, but there seems little point. They are very versitile in chaining together processes that cannot use normal command line pipes (e.g. the Oracle export above)


I hope that this is useful,

Robin
Liverpool/Blackburn
UK