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Whenever you upgrade or add a library to the system, it's not a bad idea to run ldconfig to regenerate the library cache used by ld.so. In some cases, a new library may not be recognized by ld.so until you run ldconfig.

One question remains: where can you obtain the new versions of libraries? Several of the basic system libraries (libc, libm, and so on) can be downloaded from the directory ftp://ftp.gnu.org/pub/gnu/glibc. This contains source versions of libc and related libraries. Other libraries are maintained and archived separately. At any rate, all libraries you install should include the .so.version files and possibly the .a files, as well as a set of include files for use with the compiler.

Upgrading the Compiler

One other important part of the system to keep up to date is the C compiler and related utilities. These include gcc (the GNU C and C++ compiler itself), the linker, the assembler, the C preprocessor, and various include files and libraries used by the compiler itself. All are included in the Linux gcc distribution. Usually, a new version of gcc is released along with new versions of the libc library and include files, and each requires the other.

You can find the current gcc release on the various FTP archives, including ftp://ftp.gnu.org/pub/gnu/gcc. The release notes there should tell you what to do. If you don't have Internet access, you can obtain the newest compiler from CD-ROM archives of the FTP sites, as described earlier.

To find out what version of gcc you have, use the command:

gcc -v

This should tell you something like:

Reading specs from /usr/lib/gcc-lib/i586-suse-linux/3.3.5/specs

Configured with: ../configure --enable-threads=posix --prefix=/usr --with-local-

prefix=/usr/local --infodir=/usr/share/info --mandir=/usr/share/man --enable-

languages=c,c++,f77,objc,java,ada --disable-checking --libdir=/usr/lib --enable-

libgcj --with-slibdir=/lib --with-system-zlib --enable-shared --enable-_ _cxa_atexit

i586-suse-linux

Thread model: posix

gcc version 3.3.5 20050117 (prerelease) (SUSE Linux)

The last line is the interesting one, telling you the version number of gcc and when it was released. Note that gcc itself is just a frontend to the actual compiler and code-generation tools found under

/usr/lib/gcc-lib/machine/version

gcc (usually in /usr/bin) can be used with multiple versions of the compiler proper, with the -V option. In "Programming with gcc" in Chapter 21, we describe the use of gcc in detail.

We would at this point like to warn you not to try newer compilers without knowing exactly what you are doing. Newer compilers might generate object files that are incompatible with the older ones; this can lead to all kinds of trouble. Version 3.3.x of gcc is, at the time of this writing, considered the standard compiler for Linux that everybody expects to find available, even though Versions 3.4.0 and even 4.0.0 are already available. Earlier, when one distributor (Red Hat) started to ship a newer version instead (and even that newer version was not officially released), users ran into lots of trouble. Of course, by the time you read this, another compiler version might be considered the standard. And if you feel adventurous, by all means try newer versions, just be prepared for some serious tweaking.

* * *

[*] A virus in the classic sense is a program that attaches to a "host" and runs when the host is executed. On Unix systems, this usually requires root privileges to do any harm, and if programmers could obtain such privileges, they probably wouldn't bother with a virus.

[*] On some distributions, the static versions of the libraries are moved into a separate package and not necessarily installed by default. If this is the case, you won't find the .a files unless you install them.

Archive and Compression Utilities

When installing or upgrading software on Unix systems, the first things you need to be familiar with are the tools used for compressing and archiving