clstr_rev: 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
/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 Debian possible default full paths are:

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

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