Discover how to Chroot Jail Apache in Linux with our comprehensive guide. Enhance your web server security by isolating Apache processes from the rest of the system. #centlinux #linux #apache
Table of Contents
What is Chroot Jail?
In Linux, Chroot is an operation to change the apparent root directory i.e. / for a running process and their child processes. The process running in Chroot can not access the files and commands outside that environmental directory tree. This modified environment is called a Chroot Jail.
A chroot environment is relatively difficult to set up than a traditional install, especially if we run other software like MySQL, PHP, Python, etc.
Why to Chroot Jail Apache?
By chrooting the Apache web server, we do not actually increase the security, rather we limit the access to files and commands by the httpd process and decreases the possible impact, when an Apache web server is compromised. Also potentially dangerous CGI scripts can only access the environmental root directory.
In this post, we will set up a chroot jail Apache Web Server in Linux, and create the systemd unit to auto-start the httpd service.
Note: All demonstrations in this article are CLI based, therefore, it is recommended that you should have The Linux Command Line: A Complete Introduction (PAID LINK) for quick reference.
System Specification
We are using a Linux machine with following specification for this demonstration.
- Hostname – webserver-01.example.com
- IP Address – 192.168.116.61/24
- Operating System – RHEL 7.5
Chroot Jail Apache Web Server
Connect to our Linux machine using ssh and create the directory for setting up the chroot jail.
# mkdir -p /chroot/httpd/
We have already configured the local yum repository on the machine. Please refer to my previous article Configure Local Yum Repository using ISO in Linux.
Now, we are installing Apache web server using yum, but in a non-default directory.
# yum install -y httpd --installroot=/chroot/httpd
Above command will install the Apache Web Server and its dependencies in the /chroot/httpd. You may observe that, it installs many packages that were already installed on the default root /. These packages are reinstalled in /chroot/httpd for the sake of chroot jail setup.
Create some required devices for the chroot environment.
# cd /chroot/httpd/dev # rm -f null # mknod /chroot/httpd/dev/null c 1 3 # mknod /chroot/httpd/dev/random c 1 8 # mknod /chroot/httpd/dev/urandom c 1 9 # ls -al total 0 drwxr-xr-x. 2 root root 47 Sep 2 19:26 . dr-xr-xr-x. 17 root root 224 Sep 2 19:17 .. crw-r--r--. 1 root root 1, 3 Sep 2 19:26 null crw-r--r--. 1 root root 1, 8 Sep 2 19:26 random crw-r--r--. 1 root root 1, 9 Sep 2 19:26 urandom
Add a default homepage for Apache web server.
# cd /chroot/httpd/var/www/html/ # cat >> index.html << EOF > <html> > <head> > <body> > <h1>Apache Homepage from Chroot Jail.</h1> > </body> > </html> > EOF
Allow httpd service to communicate through Firewall.
# firewall-cmd --permanent --add-service=http success # firewall-cmd --reload success
Configure systemd unit to autostart httpd service. First copy the required configuration files from chroot jail to host environment.
# cp /chroot/httpd/etc/sysconfig/httpd /etc/sysconfig/ # cp /chroot/httpd/usr/lib/systemd/system/httpd.service /usr/lib/systemd/system/
Now edit the httpd.service unit to start Apache in chrooted environment.
# vi /usr/lib/systemd/system/httpd.service
Search and update the following three lines.
Type=simple ExecStart=/sbin/chroot /chroot/httpd /usr/sbin/httpd $OPTIONS -DFOREGROUND ExecReload=/sbin/chroot /chroot/httpd /usr/sbin/httpd $OPTIONS -k graceful
For further clarification, the differences in files after editing are shown below.
# diff /chroot/httpd/usr/lib/systemd/system/httpd.service /usr/lib/systemd/system/httpd.service 8c8 < Type=notify --- > Type=simple 10,11c10,11 < ExecStart=/usr/sbin/httpd $OPTIONS -DFOREGROUND < ExecReload=/usr/sbin/httpd $OPTIONS -k graceful --- > ExecStart=/sbin/chroot /chroot/httpd /usr/sbin/httpd $OPTIONS -DFOREGROUND > ExecReload=/sbin/chroot /chroot/httpd /usr/sbin/httpd $OPTIONS -k graceful
Start and enable httpd service.
# systemctl daemon-reload # systemctl start httpd ; systemctl enable httpd Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.
Check root directory for running httpd service. First we obtain the PID of the httpd process and then check it’s root directory in the proc folder.
# systemctl status httpd
â httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
Active: active (running) since Sun 2018-09-02 20:18:23 PKT; 1min 16s ago
Docs: man:httpd(8)
man:apachectl(8)
Main PID: 10620 (httpd)
CGroup: /system.slice/httpd.service
ââ10620 /usr/sbin/httpd -DFOREGROUND
ââ10639 /usr/sbin/httpd -DFOREGROUND
ââ10640 /usr/sbin/httpd -DFOREGROUND
ââ10641 /usr/sbin/httpd -DFOREGROUND
ââ10642 /usr/sbin/httpd -DFOREGROUND
ââ10643 /usr/sbin/httpd -DFOREGROUND
Sep 02 20:18:23 webserver-01.example.com systemd[1]: Started The Apache HTTP ...
Sep 02 20:18:23 webserver-01.example.com systemd[1]: Starting The Apache HTTP...
Hint: Some lines were ellipsized, use -l to show in full.
# ls /proc/10620/root -al
lrwxrwxrwx. 1 root root 0 Sep 2 20:20 /proc/10620/root -> /chroot/httpdBrowse the URL http://webserver-01.example.com/ from a client’s browser to verify the httpd service.
We have successfully set up a chroot jail for our Apache Web Server in Linux.
Recommended Online Training: Learn Bash Shell in Linux for Beginners
Final Thoughts
Implementing a Chroot Jail for Apache in Linux can greatly improve your web server’s security by isolating its processes from the rest of the system. By following this guide, you can ensure a more secure and robust environment for your web applications.
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One issue… when I tried the initial yum install, I got this error:
Cannot find a valid baseurl for repo: base/$releasever/x86_64
When using –installroot=, the variable $releasever isn't populated. The fix is to include –releasever=7 in the command:
yum install -y httpd –releasever=7 –installroot=/chroot/httpd
After that it worked perfectly. Thanks!
Hi, its good that you resolve the issue by yourself. But the problem does not related to Chroot, rather it is caused due to the yum configuration. Please refer to Configure Local Yum Repository using ISO in RHEL 7
Hello, thanks a lot, very useful !
Can you tell how to use php in that configuration please ? Does it need to be installed in the jail ?
Thanks a lot
There are different ways to install PHP in chrooted environment. It depends upon the user requirement. But if you are following the above article, then it is better that you install PHP in the jail as well.