"emerge world" after a stage3 install

[bender_pondie]

I recently did a new stage3 install and got most everything on my system up and running. My problem is I started running into compile errors when I tried to emerge different programs. My best guess as to why is I left my "USE" tags is the make.conf blank and just used the system defaults. I went through all the USE variables and updated the make.conf with about 20 or so USE tags. I am about to do an “emerge world” to recompile everything on my system with the updated gcc compile options. I didn't want to do this until I got some type of feedback because I don't know if I'm about to F up my system something awful. Any advice would be very useful. Thank you in advance for any and all help provided.

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[moocha]

emerge -e world would be maybe a better idea Of course, with a -pv too, to get a quick visual.
Also, if I were you I'd first download all the distfiles, just in case, via emerge -fe world.
And to ensure a clean toolchain it's a good idea to first emerge -e system.
So, to sum it up:

[GuidoJ]

If you just changed teh USE flags, you should specify the "--newuse" option to emerge. That will probably save you several hours of recompiling.

OTOH I suggest you also have a look at the CFLAGS. Keep their setting conservative though, since high optimizations might result in runtime errors. If you change the CFLAGS, you should recompile everything for them to take effect (emerge -e world).

In general, you should not have to worry about doing a recompilation of everything you have installed. Many gentoo users have done it more than once.

[bender_pondie]

Thanks for the advice. I have an AMD64 system and just left the CFLAGS flag as default and don't plan on changing them. Normally I just use the "emerge -av" command when I install new programs. Should I start using different emerge switches by default? I was a slackware user for several years so dealing with portage is a new concept for me but I am starting to enjoy it.

[moocha]

-av is more interactive - so I guess it's a matter of taste.
-e means "recompile all packages from scratch, pretending no packages were installed". Takes a while, depending on your machine.
The above is usual procedure I follow when having upgraded glibc, gcc, binutils, or some important low-level static library like zlib (I'm referring to emerge -fe world, emerge -e system, emerge -e world).
The first emerge -e system causes the toolchain to be upgraded. The second emerge -e world includes an emerge -e system actually, which causes the toolchain to be recompiled yet again but this time cleanly using itself, thus ensuring any linked-in static libraries have been compiled by a clean toolchain.
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