sr: 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:

/var/spool/hylafax/bin/dict/sr - from package: hylafax+

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

On Debian possible default full paths are:

/usr/bin/sr - from package: surfraw

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

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