clstr_renumber: 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

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 Debian possible default full paths are:

/usr/bin/clstr_renumber - from package: cd-hit

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