Visit Jeremy's Blog.
Go Back > Forums > Linux Forums > Linux - Newbie
User Name
Linux - Newbie This Linux forum is for members that are new to Linux.
Just starting out and have a question? If it is not in the man pages or the how-to's this is the place!


  Search this Thread
Old 10-27-2011, 01:26 PM   #1
LQ Newbie
Registered: Oct 2011
Posts: 2

Rep: Reputation: Disabled
Executing PASSWD from an embedded C program

I am running an embedded C program on a Digi 9P 9215 module with a Linux op. system. One of the tasks I am running is telnet. I use the supplied telnet daemon and communicate with the rest of the system through shared memory to update a system menu, store in flash etc. I want to change the login password (I have set up a user admin which invokes my telnet interface) by running a shell that takes the new password from a file that I write just before running the shell. Everything appears to work except the final massage from running $passwd admin is that the password is unchanged! I am assuming it is something to do with file ownership/permissions but I cannot seem to set anything up that works. The C code and files are below;
C code
fp = fopen(PASSWORD_FILE, "w+");
//store the new password in our structure
//write to the newpwd file
//execute our shell file, chpwd - this will call newpwd
sprintf(sysCmd,"sh /etc/chpwd\n\r");
fpVal = system(sysCmd);

newpwd file

chpwd file

#file to change telnet admin password
chmod a+xrw /etc/newpwd
passwd admin < /etc/newpwd

If I follow exactly the same process from the console keyboard everything works, and the password is changed, but when executed from my program, everything appears to work except the password remains unchanged! Thus my conclusion it is something to do with permissions.

Any pointers to help me solve this would be most welcome! Thanks
Old 10-28-2011, 05:55 AM   #2
Registered: Jan 2010
Location: Velveeta, USA
Distribution: Xen, Gentoo,Ubuntu,openSUSE,Debian,pfSense
Posts: 98

Rep: Reputation: 8
passwd uses kbd device in raw mode, as opposed to "cooked", google it

I had 30-40 machines that I used to admin and occasionally changed their passwords
I used a program call "expect" written on top of tcl (only good program in tcl I ever saw)
You can write scripts as a series of "expect $", send "passwd", expect "Old Password: ", send "foobar" , etc, etc
Old 10-28-2011, 11:13 AM   #3
LQ Newbie
Registered: Oct 2011
Posts: 2

Original Poster
Rep: Reputation: Disabled
Thanks BSD. Guess I need to figure out how to install expect on my system then! Unfortunately, as a novice, that is rather more difficult than I'm sure it should be.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Executing a program in c daYz Programming 2 07-27-2007 03:34 PM
Executing program as non-root arip Programming 4 12-01-2005 05:41 AM
Writing and executing a program Russb Linux - Software 1 07-25-2004 06:49 PM
Servlets executing a C program. webee Programming 1 02-04-2003 05:19 PM
Executing a program with out system() in c++ sobdk Programming 2 11-02-2002 07:45 AM > Forums > Linux Forums > Linux - Newbie

All times are GMT -5. The time now is 03:18 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration