tmpwatch: 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/tmpwatch - from package: tmpwatch
/usr/sbin/tmpwatch - from package: tmpwatch

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

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