Magento Enable Maintenance Mode

Log in to your account using SSH and Change to the directory where you installed Magento.

Run the blow given command

touch maintenance.flag

service httpd restart

Its also possible that we can the website accessible only for some given IPs

For that edit the index.php file and assign teh IPs to the array $allowed = array(‘xxx.xxx.xxx.xxx’);

Disk Space Usage CentOs Linux

Check File System Disk Space Usage : df
Display Information of all File System Disk Space Usage : df -a
Show Disk Space Usage in Human Readable Format : df -h
Display Information of /home File System : df -hT /home
Display Information of File System in Bytes : df -k
Display Information of File System in MB : df -m
Display Information of File System in GB : df -h
Display File System Inodes : df -i
Display File System : df -T
Include Certain File System : df -t ext
Exclude Certain File System : df -x ext
Display Information of df Command: df --help