The Linux ELF HOWTO: Installation

The aim of this conversion is to leave you with a system which can build and run both a.out and ELF programs, with each type of program being able to find its appropriate breed of shared libraries. This obviously requires a bit more intelligence in the library search routines than the simple `look in /lib, /usr/lib and anywhere else that the program was compiled to search' strategy that some other systems can get away with.

The beastie responsible for searching out libraries in linux is /lib/ld.so. The compiler and linker do not encode absolute library pathnames into the programs they output; instead they put the library name and the absolute path to ld.so in, and leave ld.so to match the library name to the appropriate place at runtime. This has one very important effect --- it means that the libraries that a program uses can be moved to other directories without recompiling the program, provided that ld.so is told to search the new directory. This is essential functionality for the directory swapping operation that follows.

The corollary of the above, of course, is that any attempt to delete or move ld.so will cause every dynamically linked program on the system to stop working. This is generally regarded as a Bad Thing.

For ELF binaries, an alternate dynamic loader is provided. This is /lib/ld-linux.so.1, and does exactly the same thing as ld.so, but for ELF programs. ld-linux.so.1 uses the same support files and programs (ldd, ldconfig, and /etc/ld.so.conf) as the a.out loader ld.so does.

The basic plan, then, is that ELF development things (compilers, include files and libraries) go into /usr/{bin,lib,include} where your a.out ones currently are, and the a.out things will be moved into /usr/i486-linuxaout/{bin, lib, include}. /etc/ld.so.conf lists all the places on the system where libraries are expected to be found, and ldconfig is intelligent enough to distinguish between ELF and a.out variants.

There are a couple of exceptions to the library placement, though.

Some old programs were built without the use of ld.so. These would all cease working if their libraries were moved from under them. Thus, libc.so* and libm.so* must stay where they are in /lib, and the ELF versions have had their major numbers upgraded so that they do not overwrite the a.out ones. Old X libraries (prior to version 6) are best left where they are also, although newer ones (libX*so.6) must be moved. Moving the old ones will apparently break xview programs, and not moving the new ones will cause them to be overwritten when you install ELF X libraries. If you have non-ld.so programs that require libraries other than the above (if you know which programs they are, you can run ldd on them to find out which libraries they need before breaking them) you have essentially two options. One, you can extract the ELF library tar files into a temporary directory, check whether your precious library would be overwritten, and if so, move the ELF version of the library into, say, /usr/i486-linux/lib instead of /lib. Make sure your ld.so.conf has /usr/i486-linux/lib in it, then run ldconfig and think no more on't. Two, you can recompile or acquire a newer copy of the offending program. This might not be a bad idea, if possible.
If you have /usr and / on different partitions, you'll need to move at least some of the libraries in /lib to somewhere on the root disk, not on /usr. Either you can go through the programs that you need to run at system startup or when in single-user mode, and identify the libraries they use, or you can depend on your system/distribution integrator to have done this for you and just move all (er ... some. See above for the exceptions) of the libraries in /lib to /lib-aout.

2.2 Before you start --- Notes and Caveats

You will need to be running a post-1.1.52 kernel with ELF binary format support.
You are recommended to prepare or acquire a linux boot/root disk, such as a Slackware rescue disk. You probably won't need it, but if you do and you don't have one, you'll kick yourself. In a similar `prevention is better than cure' vein, statically linked copies of mv, ln, and maybe other file manipulation commands (though in fact I think you can do everything else you actually need to with shell builtins) may help you out of any awkward situations you could end up in.
If you have been following the ELF development, you may have ELF libraries in /lib/elf (usually libc.so.4 and co). Applications that you built using these should be rebuilt, then the directory removed. There is no need for a /lib/elf directory!
Most Linux installations these days have converged on the `FSSTND' standard file system, but doubtless there are still installed systems that haven't. If you see references to /sbin/something and you don't have a /sbin directory, you'll probably find the program referred to in /bin or /etc/.

2.3 You will need ...

The following packages are available from ftp://tsx-11.mit.edu/pub/linux/packages/GCC/ and ftp://sunsite.unc.edu/pub/Linux/GCC/. Both sites are widely mirrored; please take the time to look up your nearest mirror site and use that instead of the master sites where possible. It's faster for both you and everyone else.

These packages (either the listed version or a later one) are required. Also download and read through the release notes for each of them: these are the files named release.packagename. This applies especially if you get newer versions than are listed here, as procedures may have changed.

ld.so-1.7.3.tar.gz --- the new dynamic linker
libc-5.0.9.bin.tar.gz --- the ELF shared images for the C library and its friends (m (maths), termcap, gdbm, and so on), plus the corresponding static libraries and the include files needed to compile programs with them. libc 5.2.something is expected to be released during the lifetime of this HOWTO, and is considerably different from 5.0.9; if you want to install it, you're on your own, but I'd recommend installing 5.0.9 first and then installing it over the top. There are several parts to libc 5.0.9 which are not included in 5.2.x and for which the distribution channels are not entirely set up yet.
gcc-2.7.0.bin.tar.gz --- the ELF C compiler. Also includes an a.out C compiler which understands the new directory layout.
binutils-2.5.2l.17.bin.tar.gz --- the GNU binary utilities patched for Linux. These are programs such as gas, ld, strings and so on, most of which are required to make the C compiler go.

2.4 Rearranging your filesystem

Sooo... Note that in all that follows, when I say `remove' I naturally mean `backup then remove' :-). Also, these instructions directly apply only to people who haven't yet messed with ELF --- those who have are expected to have the necessary nous to adapt as appropriate. Let's go!

Make the new directories that you will move a.out things to



mkdir -p /usr/i486-linuxaout/bin
mkdir -p /usr/i486-linuxaout/include
mkdir -p /usr/i486-linuxaout/lib
mkdir /lib-aout

Untar the dynamic linker package ld.so-1.7.3 in the directory you usually put source code, then read through the ld.so-1.7.3/instldso.sh script just unpacked. If you have a really standard system, run it by doing sh instldso.sh, but if you have anything at all unusual then do the install by hand instead. `Anything at all unusual' includes
- using zsh as a shell (some versions of zsh define $VERSION, which seems to confuse instldso.sh)
- having symlinks from /lib/elf to /lib (which you shouldn't need, but you may have valid reasons for if you have been following the ELF development)
Edit /etc/ld.so.conf to add the new directory /usr/i486-linuxaout/lib (and /lib-aout if you're going to need one). Then rerun /sbin/ldconfig -v to check that it is picking up the new directories.
Move all the a.out libraries in /usr/*/lib to /usr/i486-linuxaout/lib. Note, I said `libraries' not `everything'. That's files matching the specification lib*.so* , lib*.sa*, or lib*.a. Don't start moving /usr/lib/gcc-lib or anything silly like that around.
Now look at /lib. Leave intact libc.so*, libm.so*, and libdl.so*. If you have symlinks to X libraries (libX*.so.3*) leave them there too --- XView and some other packages may require them. Leave ld.so*, ld-linux.so* and any other files starting with ld. As for the remaining libraries (if you have any left): if you have /usr on the root partition, put them in /usr/i486-linuxaout/lib. If you have /usr mounted separately, put them in /lib-aout. Now run ldconfig -v
Remove the directory /usr/lib/ldscripts if it's there, in preparation for installing the binutils (which will recreate it)
Remove any copies of ld and as (except for ld86 and as86) that you can find in /usr/bin.
Some versions of GNU tar appear to have problems dealing with symbolic links in the destination directory. You have two options here:
1. (preferred) Use cpio instead of tar, it doesn't have this problem. zcat /wherever/you/put/it/libc-5.0.9.tar.gz | cpio -iv is the magic incantation here, to be executed from the root directory.
2. (if you don't have cpio installed) Before installing the libc images you might want to go through /usr/include and remove some parts. This is icky. Many packages (such as ncurses) are installed into /usr/include by distribution maintainers and are not supplied with the C library. Backup the /usr/include tree, use tar tzf to see what's in the archive before untarring it, then delete the bits of /usr/include that it actually fills. Then untar the libc-5.0.9.bin.tar.gz package from root.
Install the binutils package. tar -xvzf binutils-2.5.2.l17.bin.tar.gz -C / is one perfectly good way to do this.
You have now installed everything you need to run ELF executables. Medical experts recommend that VDU workers take regular breaks away from the screen; this would be an opportune moment. Don't forget what you were doing, though; depending on the version of gcc you were previously using, you may have left yourself unable to compile programs in a.out until you unpack the new gcc.
Backup and remove everything in /usr/lib/gcc-lib/{i486-linux, i486-linuxelf, i486-linuxaout}/ If you use a non-standard gcc driver (eg if you use Gnu ADA), copy that somewhere safe also. Then install the gcc package, again by untarring from root.
Some programs (notably various X programs) use /lib/cpp, which under Linux is generally a link to /usr/lib/gcc-lib/i486-linux/version/cpp. As the preceding step wiped out whatever version of cpp it was pointing to, you'll need to recreate the link:
$ cd /lib $ ln -s /usr/lib/gcc-lib/i486-linux/2.7.0/cpp .

The FSSTND people have once again justified their keep by moving the utmp and wtmp files from /var/adm to /var/run and /var/log respectively. You'll need to add some links dependent on where they currently live, and you may need to make the /var/log and /var/adm directories too. I reproduce below the ls -l output of appropriate bits on my system:


$ ls -ld /var/adm /var/log /var/run /var/log/*tmp /var/run/*tmp
lrwxrwxrwx   1 root     root            3 May 24 05:53 /var/adm -> log/
drwxr-xr-x   9 root     root         1024 Aug 13 23:17 /var/log/
lrwxrwxrwx   1 root     root           11 Aug 13 23:17 /var/log/utmp -> ../run/utmp
-rw-r--r--   1 root     root       451472 Aug 13 23:00 /var/log/wtmp
drwxr-xr-x   2 root     root         1024 Aug 13 23:17 /var/run/
-rw-r--r--   1 root     root          448 Aug 13 23:00 /var/run/utmp

Check the FSSTND (from LDP archives such as ftp://sunsite.unc.edu/pub/Linux/docs/fsstnd/) for the full story.

This step is optional. If you're intending to continue compiling programs in a.out, this is the appropriate time to install libc.so 4.7.x. Untar it from root, as you are now no doubt fully capable of doing without further explanation.

Done! Simple tests that you can try are



$ gcc -v
Reading specs from /usr/lib/gcc-lib/i486-linux/2.7.0/specs
gcc version 2.7.0
$ gcc -v -b i486-linuxaout
Reading specs from /usr/lib/gcc-lib/i486-linuxaout/2.7.0/specs
gcc version 2.7.0
$ ld -V
ld version cygnus/linux-2.5.2l.14 (with BFD cygnus/linux-2.5.2l.11)
  Supported emulations:
   elf_i386
   i386linux
   i386coff

followed of course by the traditional ``Hello, world'' program. Try it with gcc and with gcc -b i486-linuxaout to check that both the a.out and ELF compilers are set up corectly.

2.5 What it should look like (outline directory structure)

This is a deliberately vague guide to what the files you have just installed are. It may be useful for troubleshooting or deciding what to delete.

`/lib`

Dynamic linkers ld.so (a.out) and ld-linux.so.1 (ELF). Either of these may be symlinks, but make sure that the files they point to do exist.
Basic shared libraries libc.so.4, libm.so.4 (a.out) These are symlinks, but check that they point to real files.
Basic shared libraries libc.so.5, libm.so.5, libdl.so.1,libcurses.so.1,libtermcap.so.2, (ELF). Again, these are symlinks.
Lots of symlinks. For each library, there should be an actual file (for example libc.so.5.0.9), a symlink to it with only the major version number in its name (libc.so.5) and a symlink pointing to that with no version number (libc.so). That's
lrwxrwxrwx 1 root root 9 May 24 05:52 libc.so -> libc.so.5 lrwxrwxrwx 1 root root 13 Aug 25 12:48 libc.so.5 -> libc.so.5.0.9 -rwxr-xr-x 1 bin bin 562683 May 19 04:47 libc.so.5.0.9

`/usr/lib`

All the non-library files and directories that were there previously.
libbfd.so*,libdb.so*, libgdbm.so*, ELF shared libraries. All to consist of three files as explained above in the /lib section.
libbsd.a, libgmon.a, libldso.a, libmcheck.a, libieee.a, libmcheck.a and one lib*.a file for every ELF shared library in /lib and /usr/lib . ELF static libraries. The ones duplicating the shared libraries may not be tremendously useful for most people --- when using ELF, you can use the gcc -g switch with shared libraries, so there's not much reason to compile static any longer.
crt0.o, gcrt0.o. a.out `start of program' files; one of these is linked as the first file in every a.out program you compile, unless you take steps to avoid it.
crt1.o, crtbegin.o, crtbeginS.o, crtend.o, crtendS.o, crti.o, crtn.o, gcrt1.o. ELF startup files. These do similar things to *crt0.o above for ELF programs.

`/usr/lib/ldscripts`

This is where the driver scripts for ld live, as the name suggests. It should look like



$ ls /usr/lib/ldscripts/
elf_i386.x      elf_i386.xs     i386coff.xn     i386linux.xbn
elf_i386.xbn    elf_i386.xu     i386coff.xr     i386linux.xn
elf_i386.xn     i386coff.x      i386coff.xu     i386linux.xr
elf_i386.xr     i386coff.xbn    i386linux.x     i386linux.xu

`/usr/i486-linux/bin`

ar, as, gasp, ld, nm, ranlib, strip. These are all actually symlinks to the real binutils in /usr/bin

`/usr/i486-linuxaout/bin`

as --- the a.out assembler, and gasp, its macro preprocessor
ar, ld, nm, ranlib, strip --- symlinks to the real binutils in /usr/bin

`/usr/i486-linux/lib`

ldscripts is a symlink to /usr/lib/ldscripts.

`/usr/i486-linuxaout/lib`

lib*.so*. a.out shared library images. Needed to run a.out programs
lib*.sa. a.out shared library stubs. Needed to compile a.out programs that use shared libraries. If you don't intend to, you can safely remove these.
lib*.a. a.out static libraries. Needed to compile static a.out programs (eg when compiling with -g). Again, you can delete them if you don't intend to.
ldscripts is a symbolic link to /usr/lib/ldscripts

`/usr/lib/gcc-lib/i486-linux/2.7.0`

This directory contains a version of gcc 2.7.0 set up to compile ELF programs.

`/usr/lib/gcc-lib/i486-linuxaout/2.7.0`

This directory contains a version of gcc 2.7.0 set up to compile a.out programs, which knows about the new directory structure. If you're not going to compile anything in a.out, deleting this may free up around 4Mb.

2.6 Common errors (Don't Panic!)

... in large friendly letters.

You moved the wrong thing and now nothing runs

You still have a shell running, though, and with a little ingenuity you can do an awful lot with shell builtins. Remember that echo * is an acceptable substitute for ls, and echo >>filename can be used to add lines to a file. Also, don't forget that ldconfig is linked static. If you moved, say, libc.so.4 to /lib-aout mistakenly, you can do echo "lib-aout" >>/etc/ld.so.conf ; ldconfig -v/ and be back up again. If you moved /lib/ld.so you may be able to do sln /silly/place/ld.so /lib/ld.so, if you have a statically linked ln, and probably be back up again.

no such file or directory: /usr/bin/gcc

... when you know there is such a file. This usually means that the ELF dynamic loader /lib/ld-linux.so.1 is not installed, or is unreadable for some reason. You should have installed it at around step 2 previously.

not a ZMAGIC file, skipping

from ldconfig. You have an old version of the ld.so package, so get a recent one. Again, see step 2 of the installation.

bad address

on attempting to run anything ELF. You're using kernel 1.3.x, where x<3. Upgrade to 1.3.3 or downgrade to 1.2.something

_setutent: Can't open utmp file

This message is often seen in multiples of three when you start an xterm. Go and read the FSSTND tirade near the end of the installation procedure.

gcc: installation problem, cannot exec something: No such file or directory

when attempting to do a.out compilations (something is usually one of cpp or cc1). Either it's right, or alternatively you typed


$ gcc -b -i486-linuxaout

when you should have typed


$ gcc -b i486-linuxaout

Note that the `i486' does not start with a dash.

2. Installation

2.1 Background