For silently updating the client I needed to

1. Kill all the client GUIs (tray icons) of all users
2. Stop the background service; Update the files and executables; Start the new background service
3. Start the client GUI for all currently logged in users

The silent update is done by simply calling the normal NSIS installer with a parameter that makes it non-interactive. Information about how step one is handled is in the previous post. Step two was already in the Installer. Step three remained to be solved.

For that I created a NSIS plugin which checks if the current user is the SYSTEM user. If yes, it starts the executable for all currently logged in users. If not it returns zero. It is used like this:

StrCpy $0 "$INSTDIRUrBackupClient.exe"
startplugin::start
Pop $0
${If} $0 == '0'
Exec "$INSTDIRUrBackupClient.exe"
${EndIf}

Source code is here: http://download.urbackup.org/startplugin.zip
Binary is here (for NSIS Unicode): http://download.urbackup.org/startplugin_bin.zip

There is no 64bit version of the NSIS (Nullsoft Scriptable Install System). 64Bit processes can only be terminated from 64bit processes, so all the available NSIS plugins, such as the KillProc plugin, do not work. Additionally they do not kill the processes of all users – only those of the currently logged in users – which I wanted as well.

The problem is easily solved by packing an executable into the Installer which is then extracted and called. It is used like this in the UrBackup installer:

${If} ${RunningX64}
File "data_x64KillProc.exe"
nsExec::Exec '"$INSTDIRKillProc.exe" UrBackupClient.exe'
${Else}
File "dataKillProc.exe"
nsExec::Exec '"$INSTDIRKillProc.exe" UrBackupClient.exe'
${EndIf}

The source code of that executable is available here: http://download.urbackup.org/KillProc_src.zip
The binary files here: http://download.urbackup.org/KillProc_bin.zip
It expects only one parameter: The name of the running process to kill.