Hi Reuben, I had the exact same question. Here is a message from the archives that answered my question. But you still make a good point, the replacement /usr/bin/java shell script is pointless. the alternatives system is there to allow you to install several services/packages that provide the same functionailty ( and very often the same program names) and switch between them without uninstalling either. Its most common use is to switch between sendmail and postfix, but links can be set up to cater for any package at all. How does it work? okay, the postfix/sendmail example: many programs look for a 'sendmail' binary when they want to, well, send mail. unfortunately both the sendmail and postfix packages normally provide a binary of this name, which means that if you want to switch from sendmail to postfix you would normally have to uninstall sendmail and then install postfix instead, which will involve at the very least a certain amount of downtime. On a Redhat system, these packages have been 'hacked' to provide sendmail.sendmail / sendmail.postfix (among other) binaries, so that this problem no longer exists, but how do apps know which one to call? a series of symbolic links are set up: /usr/sbin/sendmail -> /etc/alternatives/mta -> /usr/sbin/sendmail.postfix why three links instead of two? well, the other programs with clashing names also have to be dealt with, This is done using a series of 'slave' links which are automtically switched over when you change the master 'mta' link. try the alternatives command: [root@behemoth root]# alternatives --display mta mta - status is manual. link currently points to /usr/sbin/sendmail.postfix /usr/sbin/sendmail.sendmail - priority 90 slave mta-pam: /etc/pam.d/smtp.sendmail slave mta-mailq: /usr/bin/mailq.sendmail slave mta-newaliases: /usr/bin/newaliases.sendmail slave mta-rmail: /usr/bin/rmail.sendmail slave mta-rsmtp: (null) slave mta-runq: (null) slave mta-sendmail: /usr/lib/sendmail.sendmail slave mta-mailqman: /usr/share/man/man1/mailq.sendmail.1.gz slave mta-newaliasesman: /usr/share/man/man1/newaliases.sendmail.1.gz slave mta-aliasesman: /usr/share/man/man5/aliases.sendmail.5.gz slave mta-sendmailman: /usr/share/man/man8/sendmail.sendmail.8.gz /usr/sbin/sendmail.postfix - priority 30 slave mta-pam: /etc/pam.d/smtp.postfix slave mta-mailq: /usr/bin/mailq.postfix slave mta-newaliases: /usr/bin/newaliases.postfix slave mta-rmail: /usr/bin/rmail.postfix slave mta-rsmtp: (null) slave mta-runq: (null) slave mta-sendmail: (null) slave mta-mailqman: /usr/share/man/man1/mailq.postfix.1.gz slave mta-newaliasesman: /usr/share/man/man1/newaliases.postfix.1.gz slave mta-aliasesman: /usr/share/man/man5/aliases.postfix.5.gz slave mta-sendmailman: /usr/share/man/man1/sendmail.postfix.1.gz Current `best' version is /usr/sbin/sendmail.sendmail. you switch between the two systems with alternatives --set mta /usr/sbin/sendmail.sendmail (or postfix or any other that you have set up this way) or by using redhat-switch-mail wich will change the master link and the slaves will follow along like sheep. any help? ps if you want to know the command that set these things up, look at the install scripts for sendmail rpm -qp --scripts sendmail ----- Ryan Golhar Computational Biologist The Informatics Institute at The University of Medicine & Dentistry of NJ Phone: 973-972-5034 Fax: 973-972-7412 Email: golharam@xxxxxxxxx -----Original Message----- From: Reuben D. Budiardja [mailto:techlist@xxxxxxxxxxxxxxxxxxxx] Sent: Wednesday, September 08, 2004 12:55 PM To: golharam@xxxxxxxxx; General Red Hat Linux discussion list Subject: Re: java on RH AS 3.0? On Wednesday 08 September 2004 11:02, Ryan Golhar wrote: > How do you uninstall the libgcj package? I tried doing that initially > but found libgcj is required by other RPMs which in turn are required > by others as well... And I still don't understand what the heck is the link /usr/bin/java, /usr/bin/javac provided by the libgcj supposed to do. I mean, I read about the /etc/alternatives stuffs and what it supposes to do, but in all practicality, the command java and javac from Redhat do nothing. How is it suppose to work? could someone explain ? (BTW, I also just removed the symlink so my PATH would pick up my own Sun's JDK install). Thanks. RDB -- Reuben D. Budiardja Dept. Physics and Astronomy University of Tennesse, Knoxville, TN -----BEGIN GEEK CODE BLOCK----- Version: 3.12 GIT/M/MU/P/S d-(++) s: a-- C++(+++) UL++++ P-- L+++>++++ E- W+++ N+ o? K- w--- !O M- V? !PS !PE Y PGP- t+ 5 X R- tv+ b++>+++ DI D(+) G e++>++++ h+(*) r++ y->++++ ------END GEEK CODE BLOCK------ -- redhat-list mailing list unsubscribe mailto:redhat-list-request@xxxxxxxxxx?subject=unsubscribe https://www.redhat.com/mailman/listinfo/redhat-list
