stg-unnew: 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

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/stg-unnew - from package: stgit-contrib

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