disjoint_union_sep: 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/disjoint_union_sep - from package: polylib-utils

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

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