gnuattach.xemacs21: 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/gnuattach.xemacs21 - from package: xemacs21-bin

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

Error in other languages:
gnuattach.xemacs21: bevel nie gevind nie
gnuattach.xemacs21: comandă negăsită
gnuattach.xemacs21: comando não encontrado
gnuattach.xemacs21: commande introuvable
gnuattach.xemacs21: command not found
gnuattach.xemacs21: käsku ei ole
gnuattach.xemacs21: không tìm thấy lệnh
gnuattach.xemacs21: komanda nerasta
gnuattach.xemacs21: Kommando nicht gefunden.
gnuattach.xemacs21: kommandot finns inte
gnuattach.xemacs21: komut yok
gnuattach.xemacs21: nie znaleziono polecenia
gnuattach.xemacs21: níor aimsíodh an t-ordú
gnuattach.xemacs21: no se encontró la orden
gnuattach.xemacs21: no s'ha trobat l'ordre
gnuattach.xemacs21: opdracht niet gevonden
gnuattach.xemacs21: parancs nem található
gnuattach.xemacs21: perintah tidak ditemukan
gnuattach.xemacs21: príkaz nenájdený
gnuattach.xemacs21: příkaz nenalezen
gnuattach.xemacs21: команда не найдена
gnuattach.xemacs21: командата не е открита
gnuattach.xemacs21: 命令找不到
gnuattach.xemacs21: コマンドが見つかりません