pnmalias: 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/pnmalias - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmalias - from package: netpbm

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

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