4.4. Setting Up the Environment
Set up a good working environment by creating two new startup files
for the bash shell.
While logged in as user lfs, issue
the following command to create a new .bash_profile:
cat > ~/.bash_profile << "EOF"
exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash
EOF
When logged on as user lfs, the
initial shell is usually a login shell which reads the /etc/profile of the host (probably containing some
settings and environment variables) and then .bash_profile. The exec env -i.../bin/bash command in
the .bash_profile file replaces the
running shell with a new one with a completely empty environment,
except for the HOME, TERM, and PS1 variables.
This ensures that no unwanted and potentially hazardous environment
variables from the host system leak into the build environment. The
technique used here achieves the goal of ensuring a clean
environment.
The new instance of the shell is a non-login shell, which does not read, and
execute, the contents of /etc/profile
or .bash_profile files, but rather
reads, and executes, the .bashrc file
instead. Create the .bashrc file now:
cat > ~/.bashrc << "EOF"
set +h
umask 022
LFS=/mnt/lfs
LC_ALL=POSIX
LFS_TGT=$(uname -m)-lfs-linux-gnu
PATH=/usr/bin
if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
PATH=$LFS/tools/bin:$PATH
export LFS LC_ALL LFS_TGT PATH
EOF
The meaning of the settings in .bashrc
-
set +h -
The set +h command turns off bash's hash function. Hashing is ordinarily a useful feature—bash uses a hash table to remember the full path of executable files to avoid searching the
PATHtime and again to find the same executable. However, the new tools should be used as soon as they are installed. By switching off the hash function, the shell will always search thePATHwhen a program is to be run. As such, the shell will find the newly compiled tools in$LFS/toolsas soon as they are available without remembering a previous version of the same program in a different location. -
umask 022 -
Setting the user file-creation mask (umask) to 022 ensures that newly created files and directories are only writable by their owner, but are readable and executable by anyone (assuming default modes are used by the
open(2)system call, new files will end up with permission mode 644 and directories with mode 755). -
LFS=/mnt/lfs -
The
LFSvariable should be set to the chosen mount point. -
LC_ALL=POSIX -
The
LC_ALLvariable controls the localization of certain programs, making their messages follow the conventions of a specified country. SettingLC_ALLto “POSIX” or “C” (the two are equivalent) ensures that everything will work as expected in the chroot environment. -
LFS_TGT=(uname -m)-lfs-linux-gnu -
The
LFS_TGTvariable sets a non-default, but compatible machine description for use when building our cross compiler and linker and when cross compiling our temporary toolchain. More information is contained in Toolchain Technical Notes. -
PATH=/usr/bin -
Many modern linux distributions have merged
/binand/usr/bin. When this is the case, the standardPATHvariable needs just to be set to/usr/bin/for the Chapter 6 environment. When this is not the case, the following line adds/binto the path. -
if [ ! -L /bin ]; then PATH=/bin:$PATH; fi -
If
/binis not a symbolic link, then it has to be added to thePATHvariable. -
PATH=$LFS/tools/bin:$PATH -
By putting
$LFS/tools/binahead of the standardPATH, the cross-compiler installed at the beginning of Chapter 5 is picked up by the shell immediately after its installation. This, combined with turning off hashing, limits the risk that the compiler from the host be used instead of the cross-compiler. -
export LFS LC_ALL LFS_TGT PATH -
While the above commands have set some variables, in order to make them visible within any sub-shells, we export them.
![[Important]](../images/important.png)
Important
Several commercial distributions add a non-documented instantiation
of /etc/bash.bashrc to the
initialization of bash. This file has the potential
to modify the lfs user's
environment in ways that can affect the building of critical LFS
packages. To make sure the lfs
user's environment is clean, check for the presence of /etc/bash.bashrc and, if present, move it out of
the way. As the root user, run:
[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE
After use of the lfs user is
finished at the beginning of
Chapter 7, you can restore /etc/bash.bashrc (if desired).
Note that the LFS Bash package we will build in Section 8.34, “Bash-5.0”
is not configured to load or execute /etc/bash.bashrc, so this file is useless on a
completed LFS system.
Finally, to have the environment fully prepared for building the temporary tools, source the just-created user profile:
source ~/.bash_profile