modsclean: 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/modsclean - from package: bibutils

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

On Debian possible default full paths are:

/usr/bin/modsclean - from package: bibutils

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

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