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4. Preparations

created : 2010-01-27   updated : 2010-01-27
 
 
Create the required directory by running the following as root:
mkdir -v $LFS/tools
 
The next step is to create a /tools symlink on the host system. This will point to the newly-created directory on the LFS partition. Run this command as root as well:
ln -sv $LFS/tools /
 
The following link would be created :
`/tools' -> `/mnt/lfs/tools'
Adding LFS user
groupadd lfs
useradd -s /bin/bash -g lfs -m -k /dev/null lfs

 

The meaning of the command line options:
-s /bin/bash
  This makes bash the default shell for user lfs.
-g lfs
  This option adds user lfs to group lfs.
-m
  This creates a home directory for lfs.
-k /dev/null
This parameter prevents possible copying of files from a skeleton directory (default is /etc/skel) by changing the input location to the special null device.
lfs
  This is the actual name for the created group and user.
 
Grant lfs full access to $LFS/tools by making lfs the directory owner:
chown -v lfs $LFS/tools
 
If a separate working directory was created as suggested, give user lfs ownership of this directory:
chown -v lfs $LFS/sources

Next, login as user lfs. This can be done via a virtual console, through a display manager, or with the following substitute user command:

su - lfs


The “-” instructs su to start a login shell as opposed to a non-login shell. The difference between these two types of shells can be found in detail in bash(1) and info bash.
 
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 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” 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.
 
By putting /tools/bin ahead of the standard PATH, all the programs installed 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.

Finally, to have the environment fully prepared for building the temporary tools, source the just-created user profile:
source ~/.bash_profile
 
Now logout and login again, then check the LFS environment variable.
 
exit
su - lfs
echo $LFS
 
If everything is correct,  LFS should be /mnt/lfs.
 
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