Limiting Process Resource Consumption in Unix

Introduction

In a Unix-based operating system, it is important to manage the resources consumed by processes to ensure that the system runs smoothly. If a process consumes too many resources, it can cause the system to become slow or unresponsive. In some cases, it can even cause the system to crash. Therefore, it is important to be able to limit the resources that a process can consume.

There are several ways to limit the resource consumption of processes in Unix. One way is to use the ulimit command, which allows you to set limits on the resources that a process can consume. Another way is to use the cgroups feature, which allows you to group processes together and set limits on the resources that the group can consume.

Using the ulimit Command

The ulimit command is used to set limits on the resources that a process can consume. The syntax for using ulimit is as follows −

$ ulimit [option] [limit]

There are several options that you can use with ulimit, including −

• -a − This flag Displays all current limits.

• -c − This flag Limits the size of core files.

• -d − This flag Limits the size of the data segment.

• -f − This flag Limits the size of files that can be created.

• -n − This flag Limits the number of open file descriptors.

• -s − This flag Limits the size of the stack.

• -t − This flag Limits the amount of CPU time that a process can consume.

• -u − This flag Limits the number of processes that a user can run.

For example, to limit the size of core files that a process can create, you can use the following command −

$ ulimit -c 100000

This will limit the size of core files to 100,000 bytes.

To display the current limits for a process, you can use the -a option −

$ ulimit -a

This will display a list of all the current limits for the process.

Using cgroups command

Another way to limit the resource consumption of processes in Unix is to use the cgroups feature. cgroups allows you to group processes together and set limits on the resources that the group can consume.

To use cgroups, you first need to create a cgroup and add processes to it. You can do this using the cgcreate command

$ ulimit -g resource_type:cgroup_name

For example, to create a cgroup for CPU resources called mycgroup, you can use the following command

$ ulimit -g cpu:mycgroup

To add a process to a cgroup, you can use the cgclassify command

$ cgclassify -g resource_type:cgroup_name pid

For example, to add the process with PID 1234 to the mycgroup cgroup, you can use the following command

$ cgclassify -g cpu:mycgroup 1234

Once you have created a cgroup and added processes to it, you can set limits on the resources that the cgroup can consume using the cgset command

$ cgset -r resource_type=limit cgroup_name

For example, to limit the CPU usage of the mycgroup cgroup to 50%, you can use the following command

$ cgset -r cpu.cfs_quota_us=50000 mycgroup

You can also use the cgget command to view the current limits for a cgroup

$ cgget -r resource_type cgroup_name

For example, to view the current CPU limit for the mycgroup cgroup, you can use the following command

$ cgget -r cpu.cfs_quota_us mycgroup

Example

To illustrate how these commands can be used, let's say we want to limit the CPU usage of the process with PID 1234 to 50%. We can do this using the cgroups feature as follows −

cgcreate -g cpu:mycgroup
cgclassify -g cpu:mycgroup 1234
cgset -r cpu.cfs_quota_us=50000 mycgroup

We can then verify the current CPU limit for the mycgroup cgroup using the cgget command

$ cgget -r cpu.cfs_quota_us mycgroup

This will display the following output

$ cpu.cfs_quota_us: 50000

This indicates that the CPU usage of the mycgroup cgroup is limited to 50%.

Conclusion

In this article, we have discussed two methods for limiting the resource consumption of processes in Unix: using the ulimit command and using the cgroups feature. By setting limits on the resources that a process or group of processes can consume, you can ensure that the system runs smoothly and prevent resource-intensive processes from causing problems.