rexec: 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 CentOS possible default full paths are:

/usr/bin/rexec - from package: rsh

You may install the required package with command yum install {package}

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