matchbox-keyboard: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/matchbox-keyboard - from package: matchbox-keyboard

You may install the required package with command apt-get install {package}
Error in other languages:
matchbox-keyboard: bevel nie gevind nie
matchbox-keyboard: comandă negăsită
matchbox-keyboard: comando não encontrado
matchbox-keyboard: commande introuvable
matchbox-keyboard: command not found
matchbox-keyboard: käsku ei ole
matchbox-keyboard: không tìm thấy lệnh
matchbox-keyboard: komanda nerasta
matchbox-keyboard: Kommando nicht gefunden.
matchbox-keyboard: kommandot finns inte
matchbox-keyboard: komut yok
matchbox-keyboard: nie znaleziono polecenia
matchbox-keyboard: níor aimsíodh an t-ordú
matchbox-keyboard: no se encontró la orden
matchbox-keyboard: no s'ha trobat l'ordre
matchbox-keyboard: opdracht niet gevonden
matchbox-keyboard: parancs nem található
matchbox-keyboard: perintah tidak ditemukan
matchbox-keyboard: príkaz nenájdený
matchbox-keyboard: příkaz nenalezen
matchbox-keyboard: команда не найдена
matchbox-keyboard: командата не е открита
matchbox-keyboard: 命令找不到
matchbox-keyboard: コマンドが見つかりません