nearblack: 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/nearblack - from package: gdal

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

On Debian possible default full paths are:

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

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

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