fax2ps: 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/fax2ps - from package: libtiff

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

On Debian possible default full paths are:

/usr/bin/fax2ps - from package: libtiff-tools

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

Error in other languages:
fax2ps: bevel nie gevind nie
fax2ps: comandă negăsită
fax2ps: comando não encontrado
fax2ps: commande introuvable
fax2ps: command not found
fax2ps: käsku ei ole
fax2ps: không tìm thấy lệnh
fax2ps: komanda nerasta
fax2ps: Kommando nicht gefunden.
fax2ps: kommandot finns inte
fax2ps: komut yok
fax2ps: nie znaleziono polecenia
fax2ps: níor aimsíodh an t-ordú
fax2ps: no se encontró la orden
fax2ps: no s'ha trobat l'ordre
fax2ps: opdracht niet gevonden
fax2ps: parancs nem található
fax2ps: perintah tidak ditemukan
fax2ps: príkaz nenájdený
fax2ps: příkaz nenalezen
fax2ps: команда не найдена
fax2ps: командата не е открита
fax2ps: 命令找不到
fax2ps: コマンドが見つかりません