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 the
/etc/profile or .bash_profile files, but rather reads 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=/tools/bin:/bin:/usr/bin
export LFS LC_ALL LFS_TGT PATH
EOF
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 PATH time 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 the
PATH when a program is to be run. As such,
the shell will find the newly compiled tools in $LFS/tools as soon as they are available without
remembering a previous version of the same program in a different
location.
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).
The LFS variable should be set to the
chosen mount point.
The LC_ALL variable controls the
localization of certain programs, making their messages follow the
conventions of a specified country. If the host system uses a version
of Glibc older than 2.2.4, having LC_ALL
set to something other than “POSIX” or “C” (during this chapter) may cause issues if you
exit the chroot environment and wish to return later. Setting
LC_ALL to “POSIX” or “C” (the two are equivalent) ensures that
everything will work as expected in the chroot environment.
The LFS_TGT variable 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 Section 5.2,
“Toolchain Technical Notes”.
By putting /tools/bin ahead of the
standard PATH, all the programs installed
in Chapter 5
are picked up by the shell immediately after their installation.
This, combined with turning off hashing, limits the risk that old
programs are used from the host when the same programs are available
in the chapter 5 environment.
Finally, to have the environment fully prepared for building the temporary tools, source the just-created user profile:
source ~/.bash_profile