nytidy: 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/nytidy - from package: patchy

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

On Debian possible default full paths are:

/usr/bin/nytidy - from package: nypatchy

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

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