tsvnc: command not found

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/tsvnc - from package: ssvnc

You may install the required package with command apt-get install {package}

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