#### Linux From Scratch - Version 12.0-rc1

### Chapter 4. Final Preparations

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# 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`, or when switched to the `lfs` user using an su command with the “`-`” option, the initial shell is 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 new instance of the shell is a non-login shell, which does not read, and execute, the contents of the `/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 to 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. Switching off the hash function forces the shell to search the `PATH` whenever 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 cross-compilation 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 provided by 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 should 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, it must 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 is 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 preceding commands have set some variables, in order to make them visible within any sub-shells, we export them.

### Important

Several commercial distributions add an undocumented 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

When the `lfs` user is no longer needed (at the beginning of Chapter 7), you may safely restore `/etc/bash.bashrc` (if desired).

Note that the LFS Bash package we will build in Section 8.35, “Bash-5.2.15” is not configured to load or execute `/etc/bash.bashrc`, so this file is useless on a completed LFS system.

Finally, to ensure the environment is fully prepared for building the temporary tools, force the bash shell to read the new user profile:

    source ~/.bash_profile

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