unifdefall: 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/unifdefall - from package: unifdef

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