SUMMARY: How to build Mosh from source on Ubuntu 22.04 or 24.04.

Why build Mosh from source

Mosh (or Mobile Shell) is an open source project for using terminal emulators on-the-go. It's especially useful if you want to be mobile but also desire your terminal session to stay connected across network transitions and seamlessly reconnect when network conditions improve.

Unfortunately the project seems to have stalled out as of late, and many features and bug fixes seem to be stuck on an unreleased version of the code. Since the project hasn't seen movement for about 2 years, it's also got some bitrot, so it needs some finessing in order to build it on a modern platform like Ubuntu 24.04.

Basics

Basics needed for building should be something like this:

sudo apt install \
  build-essential clang cmake git automake autoconf automake libssl-dev

Build and install older protobuf release

Mosh depends on an older release protobuf, modern versions on Ubuntu will not work. First, fetch the source: 

git clone https://github.com/protocolbuffers/protobuf \
  --single-branch --branch 25.x --depth 1

Configure it:

cd protobuf
git submodule update --init --recursive
mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=/opt/protobuf25 \
  -DCMAKE_BUILD_TYPE=Release -Dprotobuf_BUILD_TESTS=OFF

Finally, build and install:

cmake --build .. --parallel
sudo cmake --install ..

Build and install Mosh

Fetch Mosh source:

git clone https://github.com/mobile-shell/mosh --single-branch --depth 1

Configure the build:

cd mosh
./autogen.sh
PKG_CONFIG_PATH=/opt/protobuf25/lib/pkgconfig \
  PATH=/opt/protobuf25/bin:$PATH \
  ./configure --prefix /opt/mosh \
    CFLAGS="-I/opt/protobuf25/include -L/opt/protobuf25/lib" \
    CXXFLAGS="-I/opt/protobuf25/include -L/opt/protobuf25/lib" \
    LDFLAGS="-L/opt/protobuf25/lib"

Run the build and install:

make -j `nproc`
sudo make install

Conclusion

Luckily mosh does not seem to dynamically link to anything except system libraries (so we don't need to tweak things like the dynamic lib search path): 

❯ ldd /opt/mosh/bin/mosh*

/opt/mosh/bin/mosh:
 not a dynamic executable

/opt/mosh/bin/mosh-client:
 linux-vdso.so.1 (0x00007b9763220000)
 libtinfo.so.6 => /lib/x86_64-linux-gnu/libtinfo.so.6 (0x00007b97631d2000)
 libcrypto.so.3 => /lib/x86_64-linux-gnu/libcrypto.so.3 (0x00007b9762600000)
 libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007b9762be4000)
 libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007b9762200000)
 libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007b9762517000)
 libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007b9762bb6000)
 libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007b9761e00000)
 /lib64/ld-linux-x86-64.so.2 (0x00007b9763222000)

/opt/mosh/bin/mosh-server:
 linux-vdso.so.1 (0x00007aa77a36e000)
 libtinfo.so.6 => /lib/x86_64-linux-gnu/libtinfo.so.6 (0x00007aa77a320000)
 libcrypto.so.3 => /lib/x86_64-linux-gnu/libcrypto.so.3 (0x00007aa779600000)
 libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007aa77a304000)
 libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007aa779200000)
 libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007aa77a21b000)
 libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007aa77a1eb000)
 libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007aa778e00000)
 /lib64/ld-linux-x86-64.so.2 (0x00007aa77a370000)

After this you should have a functioning mosh-server binary that you can use with whatever client you desire: 

❯ /opt/mosh/bin/mosh-server --version

mosh-server (mosh 1.4.0) [build 1105d48]
Copyright 2012 Keith Winstein <mosh-devel@mit.edu>
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.