watch: 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/watch - from package: procps

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

On Debian possible default full paths are:

/usr/bin/watch - from package: procps

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

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