cssort: 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/cssort - from package: csdiff

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

On Debian possible default full paths are:

/usr/bin/cssort - from package: cstocs

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

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