redshift: 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/redshift - from package: redshift

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

On Debian possible default full paths are:

/usr/bin/redshift - from package: redshift

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

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