nice: 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/nice - from package: coreutils

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

On Debian possible default full paths are:

/usr/bin/nice - from package: coreutils

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

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