Stripping

This section is optional. If the intended user is not a programmer and does not plan to do any debugging of the system software, the system's size can be decreased by some 2 GB by removing the debugging symbols, and some unnecessary symbol table entries, from binaries and libraries. This causes no real inconvenience for a typical Linux user.

Most people who use the commands mentioned below do not experience any difficulties. However, it is easy to make a mistake and render the new system unusable. So before running the strip commands, it is a good idea to make a backup of the LFS system in its current state.

A strip command with the --strip-unneeded option removes all debug symbols from a binary or library. It also removes all symbol table entries not normally needed by the linker (for static libraries) or dynamic linker (for dynamically linked binaries and shared libraries). Using --strip-debug does not remove symbol table entries that may be needed by some applications. The difference between unneeded and debug is very small. For example, an unstripped libc.a is 22.4 MB. After stripping with --strip-debug it is 5.9 MB. Using --strip-unneeded only reduces the size further to 5.8 MB.

The debugging symbols from selected libraries are compressed with Zstd and preserved in separate files. That debugging information is needed to run regression tests with valgrind or gdb later, in BLFS.

Note that strip will overwrite the binary or library file it is processing. This can crash the processes using code or data from the file. If the process running strip is affected, the binary or library being stripped can be destroyed; this can make the system completely unusable. To avoid this problem we copy some libraries and binaries into /tmp, strip them there, then reinstall them with the install command. (The related entry in the section called “Upgrade Issues” gives the rationale for using the install command here.)

Note

The ELF loader's name is ld-linux-x86-64.so.2 on 64-bit systems and ld-linux.so.2 on 32-bit systems. The construct below selects the correct name for the current architecture, excluding anything ending with g, in case the commands below have already been run.

Important

If there is any package whose version is different from the version specified by the book (either following a security advisory or satisfying personal preference), it may be necessary to update the library file name in save_usrlib or online_usrlib. Failing to do so may render the system completely unusable.

save_usrlib="$(cd /usr/lib; ls ld-linux*[^g])
             libc.so.6
             libthread_db.so.1
             libquadmath.so.0.0.0
             libstdc++.so.6.0.34
             libitm.so.1.0.0
             libatomic.so.1.2.0"

cd /usr/lib

for LIB in $save_usrlib; do
    objcopy --only-keep-debug --compress-debug-sections=zstd $LIB $LIB.dbg
    cp $LIB /tmp/$LIB
    strip --strip-debug /tmp/$LIB
    objcopy --add-gnu-debuglink=$LIB.dbg /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/lib
    rm /tmp/$LIB
done

online_usrbin="bash find strip"
online_usrlib="libbfd-2.45.1.so
               libsframe.so.2.0.0
               libhistory.so.8.3
               libncursesw.so.6.5
               libm.so.6
               libreadline.so.8.3
               libz.so.1.3.1
               libzstd.so.1.5.7
               $(cd /usr/lib; find libnss*.so* -type f)"

for BIN in $online_usrbin; do
    cp /usr/bin/$BIN /tmp/$BIN
    strip --strip-debug /tmp/$BIN
    install -vm755 /tmp/$BIN /usr/bin
    rm /tmp/$BIN
done

for LIB in $online_usrlib; do
    cp /usr/lib/$LIB /tmp/$LIB
    strip --strip-debug /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/lib
    rm /tmp/$LIB
done

for i in $(find /usr/lib -type f -name \*.so* ! -name \*dbg) \
         $(find /usr/lib -type f -name \*.a)                 \
         $(find /usr/{bin,sbin,libexec} -type f); do
    case "$online_usrbin $online_usrlib $save_usrlib" in
        *$(basename $i)* )
            ;;
        * ) strip --strip-debug $i
            ;;
    esac
done

unset BIN LIB save_usrlib online_usrbin online_usrlib

A large number of files will be flagged as errors because their file format is not recognized. These warnings can be safely ignored. They indicate that those files are scripts, not binaries.