sss_userdel: 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/sbin/sss_userdel - from package: sssd-tools

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

On Debian possible default full paths are:

/usr/sbin/sss_userdel - from package: sssd-tools

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

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