remove mounts automatically

Also combined all these little mount and cleanup helpers into one
`cleanup` script with flags.

README.md

@@ -0,0 +1,110 @@
+
+Motivation
+==========
+
+We want users to be able to use a variety of erlang programs, which means they
+need to know how to install an erlang runtime that can run our programs. On any
+given day this will have a well defined answer, but as erlang changes, and as
+our dependencies change, the exact installation process might change too. In
+order to reliably recreate the experience of a new user, on a variety of
+possible distributions, we create a collection of chroot environments, one for
+each distribution we want to document, and then use those chroot environments
+to develop and maintain install scripts.
+
+These install scripts will check *every* dependency needed, even on a totally
+fresh installation of the corresponding linux distribution, because that is
+exactly what the chroot environments will be. This means that the install
+scripts will work on any install, whether it has been used for a long time, or
+whether it is also a fresh install, if you're mining on a VPS, or custom
+hardware, or whatever else.
+
+Usage
+=====
+
+At the moment there is only one distribution, Debian, which you can test in the
+`chroot_sandboxes/debian` subdirectory. From there you can run a variety of
+posix shell scripts to create, enter, and delete chroot environments.
+
+Create Environment
+------------------
+
+cd into `debian` and run `sudo ./create_environment` to automatically download
+`debootstrap` from [debian.org](https://www.debian.org), and create a debian
+system with it. If you already have `debootstrap` installed, then that version
+will be used instead. `debootstrap` can be installed with `apt`, if you are
+already on an `apt`y system. Running `make install` in `debian/debootstrap` is
+not recommended, since your distribution's package manager won't be able to
+uninstall it for you.
+
+A minimal debian system will be created under `debian/clean_environment`, and
+then copied over to `debian/test_environment`. This way if you run
+`sudo ./create_environment` again, instead of downloading the whole
+distribution again, it can simply overwrite `test_environment` with a new
+copy, allowing rapid iteration of install scripts, run on totally fresh
+systems every time.
+
+The script also sets up the mount points and /tmp directory in
+`debian/test_environment`, each time that it is copied from
+`debian/clean_environment`. This means `debian/clean_environment` is always an
+ordinary file hierarchy with no mount points, that can be recursively deleted,
+whereas `debian/test_environment` needs to be handled more carefully, see
+[Destroy Environment](#destroy-environment) for instructions.
+
+Finally, the script will copy all install scripts in `debian/install_scripts`
+into the chroot environment, and perform the chroot itself. The chroot is
+instructed to run `install_scripts/user_setup` with this new root directory,
+and this script will install sudo, create a user with passwordless `sudo`
+rights, and `su` into that user. You can then freely test whatever scripts you
+want as that user, and leave the environment.
+
+If you don't want to do anything interactive as that user, but instead want to
+run a single script and then exit, pass that script and its arguments to
+`sudo ./create_environment` and they will be passed down into the chroot
+environment, and run instead of the default `/bin/bash` that is normally run
+by `su`. Remember that the command will be run inside the chroot environment,
+with `/home/user` as the working directory, so the script will need to be
+accessed relative to that. e.g.
+  `sudo ./create_environment ./install_scripts/your_script`
+or
+  `sudo ./create_environment ~/install_scripts/your_script`.
+
+Destroy Environment
+-------------------
+
+The `create_environment` and `enter_environment` scripts try to clean up the
+mounts that they create, and the mounts will all disappear on reboot, but just
+in case they are still present, you can run `sudo ./cleanup` to delete the
+`test_environment` safely. If you want to delete both environments and
+`debootstrap` in one go, then `sudo ./cleanup everything` will safely unmount
+`test_environment` and then delete all three directories.
+
+`cleanup` has other options too. For example, if you want to chroot into the
+environment as root, you can manually add the mount points back using
+`sudo ./cleanup add_mounts`, and then chroot in yourself. There is also
+`sudo ./cleanup mounts` to remove the mounts manually without deleting
+`test_environment`.
+
+Reuse an Existing Environment
+-----------------------------
+
+If you want to enter an environment again, run `sudo ./enter_environment`, and
+it will chroot into the environment without deleting and recreating it,
+without installing `sudo` again, and without creating a new user.
+
+To run a script, just like with `create_environment`, you can pass arguments,
+as long as the paths involved are relative to the new root and home directory.
+e.g. `sudo ./enter_environment ~/install_scripts/your_script`.
+
+If you reboot your machine, the mount points of the chroot environment will be
+missing, (unless you put them in your system-wide fstab, you sicko,) but
+`sudo ./enter_environment` will detect this and add the mount points back
+automatically.
+
+If you are iterating an install script, then it's usually more useful to just
+run the whole thing again using `create_environment`, but if you want to
+compose multiple operations together in a script outside of the chroot, or if
+you want to enter an interactive environment again after running some more
+expensive script, then this might be useful. For example, you could test
+`create_environment` itself on other distributions, by running it inside of a
+chroot.
+

debian/cleanup

@@ -0,0 +1,90 @@
+#!/bin/sh
+
+if test `id -u` -ne 0
+then
+    echo "$0 must be run as root."
+    return
+fi
+
+FRESH=clean_environment
+ROOT=test_environment
+
+add_mount() {
+    if mountpoint "$ROOT$1" > /dev/null
+    then
+        echo "$ROOT$1 already mounted."
+    else
+        echo "Mounting $1 to $ROOT$1"
+        mkdir -p "$ROOT$1"
+        mount -o bind "$1" "$ROOT$1"
+    fi
+}
+
+remove_mount() {
+    if mountpoint "$ROOT$1" > /dev/null
+    then
+        echo "Unmounting $ROOT$1"
+        umount "$ROOT$1"
+    fi
+}
+
+add_mounts() {
+    add_mount /proc
+    add_mount /sys
+    add_mount /dev
+    add_mount /dev/pts
+}
+
+remove_mounts() {
+    remove_mount /dev/pts
+    remove_mount /dev
+    remove_mount /sys
+    remove_mount /proc
+}
+
+remove_environment() {
+    if test -d "$ROOT"
+    then
+        # Call this script that automatically unmounts the mount points too.
+        remove_mounts
+        echo "Removing $ROOT"
+        rm -r "$ROOT"
+    else
+        echo "No environment found at $ROOT. Doing nothing."
+    fi
+}
+
+remove_everything() {
+    if test -d "$ROOT"
+    then
+        # Call this script that automatically unmounts the mount points too.
+        remove_environment
+    fi
+
+    if test -d "$FRESH"
+    then
+        echo "Removing $FRESH"
+        rm -r "$FRESH"
+    fi
+
+    if test -d debootstrap
+    then
+        echo "Removing debootstrap"
+        rm -r debootstrap
+    fi
+
+    if test -f debootstrap.tar.gz
+    then
+        echo "Removing debootstrap.tar.gz"
+        rm debootstrap.tar.gz
+    fi
+}
+
+case "$1" in
+    everything)  remove_everything ;;
+    mounts)      remove_mounts ;;
+    add_mounts)  add_mounts ;;
+    environment) remove_environment ;;
+    "")          remove_environment ;;
+esac
+

debian/cleanup_everything

@@ -1,32 +0,0 @@
-#!/bin/sh
-
-if test `id -u` -ne 0
-then
-    echo "$0 must be run as root."
-    return
-fi
-
-if test -d test_environment
-then
-    # Call this script that automatically unmounts the mount points too.
-    ./destroy_environment
-fi
-
-if test -d clean_environment
-then
-    echo "Removing clean_environment"
-    rm -r clean_environment
-fi
-
-if test -d debootstrap
-then
-    echo "Removing debootstrap"
-    rm -r debootstrap
-fi
-
-if test -f debootstrap.tar.gz
-then
-    echo "Removing debootstrap.tar.gz"
-    rm debootstrap.tar.gz
-fi
-

debian/create_environment

@@ -17,26 +17,26 @@ else
     ./get_debootstrap --arch i386 sid "$FRESH" http://deb.debian.org/debian/
 fi
 
-cleanup_mount() {
-    if mountpoint "$1" > /dev/null
-    then
-        echo "Unmounting $1"
-        umount "$1"
-    fi
-}
-
 if test -e "$ROOT"
 then
     echo "Existing installation found at $ROOT, removing."
-    ./destroy_environment
+    ./cleanup
 fi
 
 echo "Copying $FRESH to $ROOT."
 cp -r "$FRESH" "$ROOT"
 
 echo "Initializing $ROOT."
-mkdir -p "$ROOT/proc"
-mount proc $ROOT/proc -t proc
-mkdir -p "$ROOT/sys"
-mount sysfs $ROOT/sys -t sysfs
 
+./cleanup add_mounts
+
+# Don't bother creating a new tmpfs. We don't want to leak files in, and we
+# don't want to waste more RAM on a second tmpfs. The whole thing is
+# temporary, after all.
+chmod 1777 "$ROOT/tmp"
+
+cp -r install_scripts "$ROOT/root"
+
+chroot "$ROOT" /root/install_scripts/user_setup "$@"
+
+./cleanup mounts

debian/destroy_environment

@@ -1,28 +0,0 @@
-#!/bin/sh
-
-if test `id -u` -ne 0
-then
-    echo "$0 must be run as root."
-    return
-fi
-
-ROOT=test_environment
-
-cleanup_mount() {
-    if mountpoint "$1" > /dev/null
-    then
-        echo "Unmounting $1"
-        umount "$1"
-    fi
-}
-
-if test -e "$ROOT"
-then
-    cleanup_mount "$ROOT/proc"
-    cleanup_mount "$ROOT/sys"
-    echo "Removing $ROOT"
-    rm -r "$ROOT"
-else
-    echo "No environment found at $ROOT. Doing nothing."
-fi
-

debian/enter_environment

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+if test `id -u` -ne 0
+then
+    echo "$0 must be run as root."
+    return
+fi
+
+ROOT=test_environment
+
+if test -e "$ROOT"
+then
+    echo "Using existing environment in $ROOT."
+else
+    ./create_environment
+fi
+
+./cleanup add_mounts
+
+chroot "$ROOT" sudo -iu user "$@"
+
+./cleanup mounts

debian/install_scripts/get_erlang_zx

@@ -0,0 +1,3 @@
+#!/bin/sh
+sudo apt install erlang-base
+wget -q https://zxq9.com/projects/zomp/get_zx && bash get_zx

debian/install_scripts/user_setup

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Noninteractive, so that other scripts can install things with apt.
+export DEBIAN_FRONTEND=noninteractive
+
+# Overwrite locale setting specified before the chroot
+export LANG=C
+export LC_ALL=C
+
+# Install sudo, since most user-facing scripts will use sudo
+apt install sudo
+
+# Add a passwordless sudoer
+useradd -m -s /bin/bash -G sudo user
+passwd -d user
+echo "user ALL=(ALL) NOPASSWD:ALL" > "/etc/sudoers.d/user"
+chmod 0440 "/etc/sudoers.d/user"
+
+# Copy the install scripts into their home directory
+cp -r ~/install_scripts /home/user
+chown -R user:user /home/user/install_scripts
+
+# su to this new user... Or sudo -iu, since we want to pass in arguments too.
+cd /home/user
+sudo -iu user "$@"

debian/mountpoints

@@ -0,0 +1,25 @@
+#!/bin/sh
+
+if test `id -u` -ne 0
+then
+    echo "$0 must be run as root."
+    return
+fi
+
+ROOT=test_environment
+
+check_mount() {
+    if mountpoint "$ROOT$1" > /dev/null
+    then
+        echo "$ROOT$1 already mounted."
+    else
+        mkdir -p "$ROOT$1"
+        mount -o bind "$1" "$ROOT$1"
+    fi
+}
+
+check_mount /proc
+check_mount /sys
+check_mount /dev
+check_mount /dev/pts
+