pgmdeshadow: 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/pgmdeshadow - from package: netpbm-progs

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

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