rletopnm: command not found

Have You tried accessing the binary with the full path?

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/rletopnm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/rletopnm - from package: netpbm

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