Linux per-process resource limits - a deep Red Hat Mystery

Introduction

Linux is an open-source operating system that is popular among users and developers because of its flexibility and security. One of features that makes Linux stand out from other operating systems is its per-process resource limits. These limits ensure that a process does not use more resources than necessary and cause other processes to slow down or fail.

However, setting and managing these resource limits can be a challenging task, especially for those who are new to Linux operating system. In this article, we will take a closer look at per-process resource limits in Linux and how to set them on Red Hat Enterprise Linux.

What are per-process resource limits?

Per-process resource limits are a set of constraints that are placed on a process to limit amount of system resources that process can use. These resources include CPU time, memory, file descriptors, and more. These limits are used to prevent a single process from consuming too many resources and causing other processes to slow down or fail.

For example, if a process is using too much memory, it can cause system to start swapping, which can cause entire system to slow down. By setting a limit on amount of memory that a process can use, we can prevent this from happening.

Types of per-process resource limits

Linux has several types of per-process resource limits, each designed to limit use of a specific system resource. Some of most commonly used per-process resource limits include −

• CPU time − This limit restricts amount of CPU time a process can use.

• Memory usage − This limit restricts amount of memory a process can use.

• Open files − This limit restricts number of files a process can open.

• Network bandwidth − This limit restricts amount of network bandwidth a process can use.

• Processes − This limit restricts number of processes a user can run at a time.

Setting per-process resource limits

To set per-process resource limits in Linux, we can use "ulimit" command. "ulimit" command allows us to view and modify limits for a specific user or for all users.

For example, to view current resource limits for current user, we can use following command −

$ ulimit -a

This will display all current resource limits for current user.

To set a specific resource limit, we can use following syntax −

$ ulimit -<resource> <limit>

For example, to set maximum number of open files to 1000, we can use following command −

$ ulimit -n 1000

This will set maximum number of open files to 1000 for current user.

Managing per-process resource limits in Red Hat Enterprise Linux

In Red Hat Enterprise Linux, process of setting and managing per-process resource limits can be a bit more complex than in other Linux distributions. This is because Red Hat Enterprise Linux uses a resource control framework called Control Groups (cgroups).

Cgroups allow us to create and manage groups of processes, each with its own set of resource limits. By using cgroups, we can set resource limits for a group of processes and ensure that they do not exceed those limits.

To set per-process resource limits using cgroups in Red Hat Enterprise Linux, we need to follow these steps −

• Step 1 − Install "libcgroup" package

The "libcgroup" package provides tools needed to manage cgroups. To install "libcgroup" package, we can use following command −

$ sudo yum install libcgroup

• Step 2 − Create a new cgroup

To create a new cgroup, we can use following command −

$ sudo cgcreate -g

• Step 3 − Create a new cgroup (continued)

The "-g" option specifies name of new cgroup. We can choose any name for cgroup, but it is recommended to choose a descriptive name that reflects purpose of cgroup.

For example, to create a cgroup named "myapp" for a group of processes running an application, we can use following command −

$ sudo cgcreate -g cpu,memory,blkio,net_cls,devices:/myapp

This will create a new cgroup named "myapp" with limits on CPU usage, memory usage, block I/O, network class, and device access.

• Step 4 − Set resource limits for cgroup

Once we have created a new cgroup, we can set resource limits for cgroup using "cgset" command.

For example, to set a limit of 512 MB of memory usage for "myapp" cgroup, we can use following command −

$ sudo cgset -r memory.limit_in_bytes=536870912 myapp

This will set a limit of 512 MB of memory usage for processes in "myapp" cgroup.

• Step 5 − Add processes to cgroup

To add processes to cgroup, we can use "cgclassify" command.

For example, to add a process with PID 1234 to "myapp" cgroup, we can use following command −

$ sudo cgclassify -g cpu,memory,blkio,net_cls,devices:myapp 1234

This will add process with PID 1234 to "myapp" cgroup and enforce resource limits set for cgroup.

Conclusion

Per-process resource limits are an essential feature of Linux that ensures that a process does not use more resources than necessary and cause other processes to slow down or fail. In Red Hat Enterprise Linux, process of setting and managing per-process resource limits can be a bit more complex due to use of cgroups.

However, by following steps outlined in this article, we can create and manage cgroups in Red Hat Enterprise Linux and set resource limits for groups of processes. By doing so, we can ensure that our applications and processes run smoothly and do not impact performance of other processes on system.