On my sort-of clean Ubuntu 20.04.3 LTS system, compiling the webserver example hangs without showing an error message or explaining why it hangs.

Steps to reproduce:

1. Clean your ruby installation, assume we are using ruby for the first time for this example:

   user@box:~$ sudo apt purge ruby
   [sudo] password for user: 
   [...]
   The following packages were automatically installed and are no longer required:
     fonts-lato ruby-minitest ruby-net-telnet ruby-power-assert ruby-test-unit ruby-xmlrpc ruby2.7-doc rubygems-integration
   Use 'sudo apt autoremove' to remove them.
   The following packages will be REMOVED:
     bundler* libruby2.7* rake* ruby* ruby-bundler* ruby-dev* ruby-molinillo* ruby-net-http-persistent* ruby-thor* ruby2.7* ruby2.7-dev*
   0 upgraded, 0 newly installed, 11 to remove and 0 not upgraded.
   After this operation, 21,1 MB disk space will be freed.
   Do you want to continue? [Y/n] 
   [...]
   dpkg: warning: while removing ruby2.7, directory '/var/lib/gems/2.7.0' not empty so not removed
   [...]
   user@box:~$ sudo rm -rf /var/lib/gems/2.7.0
   user@box:~$ sudo apt install bundler
   [...]
   The following additional packages will be installed:
     libruby2.7 rake ruby ruby-bundler ruby-dev ruby-molinillo ruby-net-http-persistent ruby-thor ruby2.7 ruby2.7-dev
   Suggested packages:
     ri
   The following NEW packages will be installed:
     bundler libruby2.7 rake ruby ruby-bundler ruby-dev ruby-molinillo ruby-net-http-persistent ruby-thor ruby2.7 ruby2.7-dev
   0 upgraded, 11 newly installed, 0 to remove and 0 not upgraded.
   Need to get 4.240 kB of archives.
   After this operation, 21,1 MB of additional disk space will be used.
   Do you want to continue? [Y/n]
   

2. Follow the webserver example

   user@box:~/sel4-webserver-arm$ repo init -u https://github.com/SEL4PROJ/sel4webserver-manifest.git
   user@box:~/sel4-webserver-arm$ repo sync
   user@box:~/sel4-webserver-arm$ mkdir build
   user@box:~/sel4-webserver-arm$ cd build
   user@box:~/sel4-webserver-arm/build$ ../init-build.sh -DPLATFORM=qemu-arm-virt
   user@box:~/sel4-webserver-arm/build$ ninja
   

3. The installation is hanging somewhere around the steps lighttpd or linux_out.
4. Checking the processes, the installer is blocking on expecting me to provide my sudo password:

   user@box:~$ ps auxf
   [...]
   user        3283  0.0  0.0  11352  5684 pts/1    Ss   10:03   0:00  |   \_ bash
   user       32547  0.0  0.0   9932  7324 pts/1    S+   10:15   0:00  |   |   \_ ninja
   user       36606  0.0  0.0   2616   540 pts/1    T    10:15   0:00  |   |       \_ /bin/sh -c cd /home/user/sel4-webserver-arm/build/docsite-prefix/src/docsite && make build
   user       36608  0.0  0.0   8940  2780 pts/1    T    10:15   0:00  |   |           \_ make build
   user       41264  0.2  0.3 2299292 174908 pts/1  Tl   10:16   0:02  |   |               \_ /usr/bin/ruby /usr/bin/bundle install
   user       41314  0.0  0.0   2620   604 pts/1    T    10:16   0:00  |   |                   \_ sh -c sudo -k -p "  Your user account isn't allowed to install to the system RubyGems.   You can cancel this ins
   root       41315  0.0  0.0  11760  4492 pts/1    T    10:16   0:00  |   |                       \_ sudo -k -p   Your user account isn't allowed to install to the system RubyGems.   You can cancel this instal
   
   

   user@box:~$ cat /proc/41314/cmdline
   sh-csudo -k -p "
   
   Your user account isn't allowed to install to the system RubyGems.
     You can cancel this installation and run:
   
         bundle install --path vendor/bundle
   
     to install the gems into ./vendor/bundle/, or you can enter your password
     and install the bundled gems to RubyGems using sudo.
   
     Password: " true
   

5. Unfortunately, it even looks like the non-interactive install pipeline is setup in a nice way where stdin is wired to /dev/null and I cannot simply pipe my password to stdin via the proc file descriptor:

   user@box:~$ ls -lah /proc/41314/fd
   total 0
   dr-x------ 2 user user  0 Okt 17 10:35 .
   dr-xr-xr-x 9 user user  0 Okt 17 10:16 ..
   lr-x------ 1 user user 64 Okt 17 10:35 0 -> /dev/null
   l-wx------ 1 user user 64 Okt 17 10:35 1 -> 'pipe:[69249]'
   l-wx------ 1 user user 64 Okt 17 10:35 2 -> 'pipe:[69249]'
   

6. The installation hangs and it is not obvious how to continue.

As a workaround to continue, I did a alias yolo='sudo /usr/sbin/visudo' && yolo and added user ALL=(ALL) NOPASSWD: ALL (where user is my username) at the bottom of the file.

Building for qemu-arm-virt fails:

~/sel4-webserver-arm$ mkdir build/
~/sel4-webserver-arm$ cd build/
~/sel4-webserver-arm/build$ ../init-build.sh -DPLATFORM=qemu-arm-virt
loading initial cache file /home/user/sel4-webserver-arm/projects/webserver/settings.cmake
-- Found seL4: /home/user/sel4-webserver-arm/kernel  
-- Default cpu specified for virt board: cortex-a53
-- QEMU MEMORY is: 2048
CMake Error at /home/user/sel4-webserver-arm/kernel/src/plat/qemu-arm-virt/config.cmake:73 (string):
  string sub-command STRIP requires two arguments.
Call Stack (most recent call first):
  /home/user/sel4-webserver-arm/kernel/configs/seL4Config.cmake:195 (include)
  /home/user/sel4-webserver-arm/kernel/FindseL4.cmake:21 (include)
  settings.cmake:84 (sel4_configure_platform_settings)


-- 
-- Default cpu specified for virt board: cortex-a53
-- QEMU MEMORY is: 2048
CMake Error at /home/user/sel4-webserver-arm/kernel/src/plat/qemu-arm-virt/config.cmake:73 (string):
  string sub-command STRIP requires two arguments.
Call Stack (most recent call first):
  /home/user/sel4-webserver-arm/kernel/configs/seL4Config.cmake:195 (include)
  /home/user/sel4-webserver-arm/kernel/FindseL4.cmake:21 (include)
  settings.cmake:84 (sel4_configure_platform_settings)
  CMakeLists.txt:14 (include)


-- 
-- The C compiler identification is GNU 9.3.0
-- The ASM compiler identification is GNU
-- Found assembler: /usr/bin/aarch64-linux-gnu-gcc
-- Check for working C compiler: /usr/bin/aarch64-linux-gnu-gcc
-- Check for working C compiler: /usr/bin/aarch64-linux-gnu-gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Found camkes-arm-vm: /home/user/sel4-webserver-arm/projects/camkes-arm-vm  
-- Found camkes-tool: /home/user/sel4-webserver-arm/projects/camkes-tool  
-- Found global-components: /home/user/sel4-webserver-arm/projects/global-components  
-- Found camkes-vm: /home/user/sel4-webserver-arm/projects/camkes-vm  
-- Found camkes-vm-images: /home/user/sel4-webserver-arm/projects/camkes-vm-images  
-- Found sel4_projects_libs: /home/user/sel4-webserver-arm/projects/seL4_projects_libs  
-- Found elfloader-tool: /home/user/sel4-webserver-arm/tools/seL4/elfloader-tool  
-- Found musllibc: /home/user/sel4-webserver-arm/projects/musllibc  
-- Found util_libs: /home/user/sel4-webserver-arm/projects/util_libs  
-- Found seL4_libs: /home/user/sel4-webserver-arm/projects/seL4_libs  
-- Found projects_libs: /home/user/sel4-webserver-arm/projects/projects_libs  
-- Found capdl: /home/user/sel4-webserver-arm/projects/capdl  
-- /home/user/sel4-webserver-arm/build/kernel/gen_headers/plat/machine/devices_gen.h is out of date. Regenerating from DTB...
WARNING:root:Only mapping 4096/65536 bytes from node /intc@8000000, region 0. Set kernel_size in YAML to silence.
WARNING:root:Only mapping 4096/65536 bytes from node /intc@8000000, region 1. Set kernel_size in YAML to silence.
WARNING:root:Only mapping 4096/65536 bytes from node /intc@8000000, region 2. Set kernel_size in YAML to silence.
interrupts for device /pl011@9000000
interrupts for device /intc@8000000
interrupts for device /timer
-- CPIO test cpio_reproducible_flag PASSED
-- Detecting cached version of: capDL-tool
-- Found Git: /usr/bin/git (found version "2.25.1") 
--   Found valid cache entry for capDL-tool
-- Found sel4runtime: /home/user/sel4-webserver-arm/projects/sel4runtime  
-- Performing Test compiler_arch_test
-- Performing Test compiler_arch_test - Success
-- libmuslc architecture: 'aarch64' (from KernelSel4Arch 'aarch64')
-- Detecting cached version of: musllibc
--   Not found cache entry for musllibc - will build from source
BenchUtiliz not available, as KernelArmExportPMUUser is OFF
-- Found camkes-vm-linux: /home/user/sel4-webserver-arm/projects/camkes-vm-linux  
-- Found lighttpd: /home/user/sel4-webserver-arm/projects/webserver/lighttpd  
-- Found docsite: /home/user/sel4-webserver-arm/projects/webserver/docsite  
-- /home/user/sel4-webserver-arm/build/ast.pickle is out of date. Regenerating...
-- /home/user/sel4-webserver-arm/build/camkes-gen.cmake is out of date. Regenerating...
-- Configuring incomplete, errors occurred!
See also "/home/user/sel4-webserver-arm/build/CMakeFiles/CMakeOutput.log".

Going to the specified file sel4-webserver-arm/kernel/src/plat/qemu-arm-virt/config.cmake:73, I see:

string(STRIP ${QEMU_OUTPUT_MESSAGE} QEMU_OUTPUT_MESSAGE)

Replacing this line with

string(STRIP "${QEMU_OUTPUT_MESSAGE}" QEMU_OUTPUT_MESSAGE)

makes the build succeed for me.