tar not reading if output directed to /dev/null Post: 302351501

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Operating Systems Linux Ubuntu tar not reading if output directed to /dev/null Post 302351501 by bakunin on Tuesday 8th of September 2009 06:57:21 PM

09-08-2009

Registered User

First off, I'd like to state that i do NOT have a problem. I just want to achieve a better understanding. So you don't need to tell me workarounds, as i have already found one.

Quote:

Originally Posted by thegeek

Before that why you would want to tar and check the integrity, better you can do by reading all the files !!

This is exactly what i was expecting tar to do: read all the files.

Quote:

Originally Posted by methyl

The parameter after "-f" is the archive filename. A value of "-" when there is no pipeline has no sensible meaning

Sorry, but this is simply not true: the dash as a filename is signifying <stdout> and if i use a redirection or a pipeline to manipulate tars output further should make no difference.

In fact (as i have stated in my first post) the command worked the way i wrote it when i used a real file (instead of /dev/null) as output destination. It is this inconsistency - the command reading all the files when a real file is the destination and not working, when the destination is /dev/null - i want to understand.

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LEARN ABOUT OPENSOLARIS

chroot

chroot(1M)						  System Administration Commands						chroot(1M)

NAME

       chroot - change root directory for a command

SYNOPSIS

       /usr/sbin/chroot newroot command

DESCRIPTION

       The  chroot  utility causes command to be executed relative to newroot. The meaning of any initial slashes (/) in the path names is changed
       to newroot for command and any of its child processes. Upon execution, the initial working directory is newroot.

       Notice that redirecting the output of command to a file,

	 chroot newroot command >x

       will create the file x relative to the original root of command, not the new one.

       The new root path name is always relative to the current root. Even if a chroot is currently in effect, the newroot argument is relative to
       the current root of the running process.

       This command can be run only by the super-user.

RETURN VALUES

       The exit status of chroot is the return value of command.

EXAMPLES

       Example 1 Using the chroot Utility

       The  chroot  utility  provides an easy way to extract tar files (see tar(1)) written with absolute filenames to a different location. It is
       necessary to copy the shared libraries used by tar (see ldd(1)) to the newroot filesystem.

	 example# mkdir /tmp/lib; cd /lib
	 example# cp ld.so.1 libc.so.1 libcmd.so.1 libdl.so.1 
		  libsec.so.1 /tmp/lib
	 example# cp /usr/bin/tar /tmp
	 example# dd if=/dev/rmt/0 | chroot /tmp tar xvf -

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cd(1), tar(1), chroot(2), ttyname(3C), attributes(5)

NOTES

       Exercise extreme caution when referencing device files in the new root file system.

       References by routines such as ttyname(3C) to stdin, stdout, and stderr will find that the device associated with the  file  descriptor	is
       unknown after chroot is run.

SunOS 5.11							    15 Dec 2003 							chroot(1M)

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