6.6. Creating Essential Files and Symlinks

#### Linux From Scratch - Version 7.10-rc1

### Chapter 6. Installing Basic System Software

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# 6.6. Creating Essential Files and Symlinks

Some programs use hard-wired paths to programs which do not exist yet. In order to satisfy these programs, create a number of symbolic links which will be replaced by real files throughout the course of this chapter after the software has been installed:

    ln -sv /tools/bin/{bash,cat,echo,pwd,stty} /bin
    ln -sv /tools/bin/perl /usr/bin
    ln -sv /tools/lib/libgcc_s.so{,.1} /usr/lib
    ln -sv /tools/lib/libstdc++.so{,.6} /usr/lib
    sed 's/tools/usr/' /tools/lib/libstdc++.la > /usr/lib/libstdc++.la
    ln -sv bash /bin/sh

The purpose of each link:

``/bin/bash``

  Many bash scripts specify `/bin/bash`.

``/bin/cat``

  This pathname is hard-coded into Glibc's configure script.

``/bin/echo``

  This is to satisfy one of the tests in Glibc's test suite, which expects `/bin/echo`.

``/bin/pwd``

  Some configure scripts, particularly Glibc's, have this pathname hard-coded.

``/bin/stty``

  This pathname is hard-coded into Expect, therefore it is needed for Binutils and GCC test suites to pass.

``/usr/bin/perl``

  Many Perl scripts hard-code this path to the perl program.

``/usr/lib/libgcc_s.so{,.1}``

  Glibc needs this for the pthreads library to work.

``/usr/lib/libstdc++{,.6}``

  This is needed by several tests in Glibc's test suite, as well as for C++ support in GMP.

``/usr/lib/libstdc++.la``

  This prevents a `/tools` reference that would otherwise be in `/usr/lib/libstdc++.la` after GCC is installed.

``/bin/sh``

  Many shell scripts hard-code `/bin/sh`.

Historically, Linux maintains a list of the mounted file systems in the file `/etc/mtab`. Modern kernels maintain this list internally and exposes it to the user via the `/proc` filesystem. To satisfy utilities that expect the presence of `/etc/mtab`, create the following symbolic link:

    ln -sv /proc/self/mounts /etc/mtab

In order for user `root` to be able to login and for the name “root” to be recognized, there must be relevant entries in the `/etc/passwd` and `/etc/group` files.

Create the `/etc/passwd` file by running the following command:

    cat > /etc/passwd << "EOF"
    root:x:0:0:root:/root:/bin/bash
    bin:x:1:1:bin:/dev/null:/bin/false
    daemon:x:6:6:Daemon User:/dev/null:/bin/false
    messagebus:x:18:18:D-Bus Message Daemon User:/var/run/dbus:/bin/false
    nobody:x:99:99:Unprivileged User:/dev/null:/bin/false
    EOF

The actual password for `root` (the “x” used here is just a placeholder) will be set later.

Create the `/etc/group` file by running the following command:

    cat > /etc/group << "EOF"
    root:x:0:
    bin:x:1:daemon
    sys:x:2:
    kmem:x:3:
    tape:x:4:
    tty:x:5:
    daemon:x:6:
    floppy:x:7:
    disk:x:8:
    lp:x:9:
    dialout:x:10:
    audio:x:11:
    video:x:12:
    utmp:x:13:
    usb:x:14:
    cdrom:x:15:
    adm:x:16:
    messagebus:x:18:
    systemd-journal:x:23:
    input:x:24:
    mail:x:34:
    nogroup:x:99:
    users:x:999:
    EOF

The created groups are not part of any standard—they are groups decided on in part by the requirements of the Udev configuration in this chapter, and in part by common convention employed by a number of existing Linux distributions. In addition, some test suites rely on specific users or groups. The Linux Standard Base (LSB, available at http://www.linuxbase.org) recommends only that, besides the group `root` with a Group ID (GID) of 0, a group `bin` with a GID of 1 be present. All other group names and GIDs can be chosen freely by the system administrator since well-written programs do not depend on GID numbers, but rather use the group's name.

To remove the “I have no name!” prompt, start a new shell. Since a full Glibc was installed in Chapter 5 and the `/etc/passwd` and `/etc/group` files have been created, user name and group name resolution will now work:

    exec /tools/bin/bash --login +h

Note the use of the `+h` directive. This tells bash not to use its internal path hashing. Without this directive, bash would remember the paths to binaries it has executed. To ensure the use of the newly compiled binaries as soon as they are installed, the `+h` directive will be used for the duration of this chapter.

The login, agetty, and init programs (and others) use a number of log files to record information such as who was logged into the system and when. However, these programs will not write to the log files if they do not already exist. Initialize the log files and give them proper permissions:

    touch /var/log/{btmp,lastlog,faillog,wtmp}
    chgrp -v utmp /var/log/lastlog
    chmod -v 664  /var/log/lastlog
    chmod -v 600  /var/log/btmp

The `/var/log/wtmp` file records all logins and logouts. The `/var/log/lastlog` file records when each user last logged in. The `/var/log/faillog` file records failed login attempts. The `/var/log/btmp` file records the bad login attempts.

### Note

The `/run/utmp` file records the users that are currently logged in. This file is created dynamically in the boot scripts.

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