gdalwarp: 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/gdalwarp - from package: gdal

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

On Debian possible default full paths are:

/usr/bin/gdalwarp - from package: gdal-bin

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

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