Hi, On Thu, 2009-09-17 at 08:09 +1000, Cameron Simpson wrote: > On 16Sep2009 19:43, devi <devi@xxxxxxxxxxx> wrote: > | On Wed, 2009-09-16 at 11:18 +0100, Dave Mitchell wrote: > | > On Wed, Sep 16, 2009 at 03:06:09PM -0400, devi wrote: > | > > The command > | > > echo "service httpd status " > /dev/pts/1 is executed on one terminal, > | > > let us assume it as t1. > | > > The echo command is executed on t1 but the output(service httpd status" > | > > is directed to /dev/pts/1 terminal. > | > > > | > > What I am saying is that the output is redirected directly to the > | > > terminal /dev/pts1/1. > | > > The output here is "service httpd status", which is generally a command. > | > > And so it gets executed. > | > > | > No, the text just appears in the terminal associated with /dev/pts1/1; > | > it does not not cause the command to be executed. That is to say, > | > you can't use this as a mechanism to insert characters into a another > | > terminal's input buffer. > | > > | But the command got executed, and it gave the status of apache > | on /dev/pts/1 terminal. > > That's quite interesting. It should _not_ cause the command to be > executed, and I really believe something more is going on. > > /dev/pts/1 is the "slave" side of the pseudoterminal; all pseudoterminals > have a "master" side and a "slave" side. Here, the /dev/pts/1 is the tty of a virtual machine. This virtual machine is created by xen. Yes, I have come across master and slave pseudo terminals, but I have not set any anything like that. > > The slave side is the "normal" terminal side that programs are connected to. > Writing to it causes text to the displayed, and reading from it consumes text > that is typed. > > The master side is what terminal emulators like xterm use. Xterm is a > GUI program that displays a terminal on your screen. When you type at > the displayed GUI, xterm catches that and writes data to the _master_ > side of the pseudo terminal it obtained. That stuff appears as though > typed to ordinary programs on the slave side. Conversely, data _read_ by > xterm from the master side is the data _written_ to the slave side; > xterm gathers that and updates the GUI, thus displaying the program > output. > > See "man ptmx" for how a pseudo terminal is obtained under Linux. > > Anyway, because of this scheme nothing you write to /dev/pts/1, a slave > device, should cause it to be _typed_ at that terminal. > > Can you confirm your setup in more detail? There is no setup, I created the virtual machine, and then found its tty. and executed the command from other terminal "t1" as specified earlier. > > I would imagine that you have two terminals open, with plain shells in > them. Typing the command "tty" in each will tell you their names, and > presumably one says "/dev/pts/1". The other is "t1". > > And you are really typing: > echo "service httpd status" >/dev/pts/1 > in the "t1" terminal, and on the /dev/pts/1 terminal you are not seeing the > string "service httpd status" displayed as plain output; instead you are > seeing the output of the command: > service httpd status > > Is that all correct? > > Can I suggest the following experiments? > > First, run the command "set -x" in the shell on /dev/pts/1. That will turn > of execution tracing, and it should then be more obvious is that shell > is really executing the command. Type some commands in that shell, like > "date" or "uptime" to see the effect. Then do your echo statement from > "t1" again. > > Secondly, on the "t1" terminal, run the command: > echo -n "service httpd status" >/dev/pts/1 > You should see it displayed on /dev/pts/1 but it won't run a command > because we have not sent the end-of-line. If you're right, it will be > as though typed, and you can go to the other terminal and edit the line > and change it before pressing enter. I have done, what you suggested, it's the same. Anyways my requirement is that, after the command is executed on /dev/pts/1, I should be able to get the return value on the terminal "t1" eg: rc=`echo "service httpd status" > /dev/pts/1" I thought rc will hold the return value, but it displays nothing. > > Cheers, > -- > Cameron Simpson <cs@xxxxxxxxxx> DoD#743 > http://www.cskk.ezoshosting.com/cs/ > > It's a vague science. - Rory Tate, circle researcher. > -- fedora-list mailing list fedora-list@xxxxxxxxxx To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list Guidelines: http://fedoraproject.org/wiki/Communicate/MailingListGuidelines
