pgmhist: 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/pgmhist - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pgmhist - from package: netpbm

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

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