usleep: 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:

/bin/usleep - from package: initscripts

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

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