rearj: 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/rearj - from package: arj

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

On Debian possible default full paths are:

/usr/bin/rearj - from package: arj

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

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