realksh.c: 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/sbin/realksh.c - from package: binfmtc

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

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