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
CONFIG_SITE=$LFS/usr/share/config.site
export LFS LC_ALL LFS_TGT PATH CONFIG_SITE
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 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 $LFS/tools/bin
as soon as they are available
without remembering a previous version of the same program
provided by the host distro, in /usr/bin
or /bin
.
umask
022
Setting the user file-creation mask (umask) to 022 ensures that
newly created files and directories are only writable by their
owner, but are readable and executable by anyone (assuming
default modes are used by the open(2)
system call, new files will end up
with permission mode 644 and directories with mode 755).
LFS=/mnt/lfs
The LFS
variable should be set to
the chosen mount point.
LC_ALL=POSIX
The LC_ALL
variable controls the
localization of certain programs, making their messages follow
the conventions of a specified country. Setting LC_ALL
to “POSIX”
or “C” (the two are equivalent) ensures
that everything will work as expected in the chroot
environment.
LFS_TGT=(uname
-m)-lfs-linux-gnu
The LFS_TGT
variable sets a
non-default, but compatible machine description for use when
building our cross compiler and linker and when cross compiling
our temporary toolchain. More information is contained in
Toolchain Technical
Notes.
PATH=/usr/bin
Many modern linux distributions have merged /bin
and /usr/bin
. When this is the case, the standard
PATH
variable needs just to be set
to /usr/bin/
for the Chapter 6
environment. When this is not the case, the following line adds
/bin
to the path.
if [ ! -L /bin ];
then PATH=/bin:$PATH; fi
If /bin
is not a symbolic link,
then it has to be added to the PATH
variable.
PATH=$LFS/tools/bin:$PATH
By putting $LFS/tools/bin
ahead
of the standard PATH
, the
cross-compiler installed at the beginning of Chapter 5
is picked up by the shell immediately after its installation.
This, combined with turning off hashing, limits the risk that
the compiler from the host be used instead of the
cross-compiler.
CONFIG_SITE=$LFS/usr/share/config.site
In Chapter 5
and Chapter 6,
if this variable is not set, configure scripts may attempt
to load configuration items specific to some distributions from
/usr/share/config.site
on the
host system. Override it to prevent potential contamination
from the host.
export
...
While the above commands have set some variables, in order to make them visible within any sub-shells, we export them.
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-5.1.16” 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