RE: /etc/alternatives

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To: "'Wayne Pinette'" <Wpinette@cariboo.bc.ca>, <redhat-list@redhat.com>, <stuart@sjsears.com>
Date: Mon, 30 Aug 2004 23:18:29 -0400

I just going to delete /usr/bin/java, /usr/bin/javac, and /usr/bin/jar.

The default installation of Sun's Java SDK will be picked up in the PATH
in /usr/java/j2sdk...

Thanks for your help...

Ryan

-----Original Message-----
From: Wayne Pinette [mailto:Wpinette@cariboo.bc.ca]
Sent: Monday, August 30, 2004 3:51 PM
To: redhat-list@redhat.com; stuart@sjsears.com; golharam@umdnj.edu
Subject: RE: /etc/alternatives

Well, quite frankly, Im still old school. I always soft link java,
javac etc to /usr/local/java/bin .. directory, and my /usr/local/java
directory is always softlinked to what ever latest and greatest version
of java I just installed. In short, I bypass alternatives. You may
want to try something like that.

Wayner

>>> Ryan Golhar <golharam@umdnj.edu> 30/08/2004 12:00:42 pm >>>
Thanks for the info. So, I'm trying to set java (in
/usr/java/j2sdk1.4.2_04/bin/java) to be the default generic java that
gets run. I tried

/usr/sbin/alternatives --set java /usr/java/j2sdk1.4.2_04/bin/java

But received the error

/usr/java/j2sdk1.4.2_04/bin/java has not been configured as an
alternative for java

So, I tried installing it using

/usr/sbin/alternatives --install java java
/usr/java/j2sdk1.4.2_04/bin/java 200

But that's not working, and I'm not sure what the problem is. (I also
must admit I'm not spending enough time trying to figure it out). Do
you know how I can get Sun's java from their JDK working again?
Thanks,

Ryan

-----Original Message-----
From: Stuart Sears [mailto:stuart@sjsears.com]
Sent: Wednesday, August 11, 2004 2:56 AM
To: golharam@umdnj.edu; General Red Hat Linux discussion list
Subject: Re: /etc/alternatives

On Wednesday 11 August 2004 04:05, Ryan Golhar wrote:
> I installed the java SDK RPM from java.sun.com.
>
> Recently, however, I noticed that /usr/bin/java, /usr/bin/javac, and

> /usr/bin/jar point to scripts in /etc/alternatives.
>
> I figured out that these replacements are from libgcj. It doesn't
> look like I can until this other RPM as there are others that depend

> on it. My question is why do they replace a legitimate program (java)

> with a script that doesn't do anything. That just seems to break
> everything. I remove the link so the real java program is picked up
> correctly. Does anyone know what this is for and why its done?
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

HTH

-- 
Stuart Sears RHCE, RHCX
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• Previous message: Harry Hoffman: "RAID 1+0 using LVM?"
• Maybe in reply to: Ryan Golhar: "/etc/alternatives"
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