psblack: 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/psblack - from package: ncl

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

On Debian possible default full paths are:

/usr/bin/psblack - from package: ncl-ncarg

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

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