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The maximum number of file limits for Linux ulimit

One: description

Linux for each user, the system limits the maximum number of processes. In order to improve performance, you can set the maximum number of processes for each linux user according to the device resources. You can use ulimit-a to display the current user process limits.

Ulimit: displays (or sets) the limit (limit) of resources available to the user, which is divided into soft limit (current limit) and hard limit (upper limit), where the hard limit is the upper limit of the soft limit, the system resources used by the application do not exceed the corresponding soft limit, and any excess will lead to the termination of the process.

[root@hadoop001] # ulimit-a

Core file size (blocks,-c) 0

Data seg size (kbytes,-d) unlimited

Scheduling priority (- e) 0

File size (blocks,-f) unlimited

Pending signals (- I) 15088

Max locked memory (kbytes,-l) 64

Max memory size (kbytes,-m) unlimited

Open files (- n) 65535

Pipe size (512 bytes,-p) 8

POSIX message queues (bytes,-Q) 819200

Real-time priority (- r) 0

Stack size (kbytes,-s) 8192

Cpu time (seconds,-t) unlimited

Max user processes (- u) 15088

Virtual memory (kbytes,-v) unlimited

File locks (- x) unlimited

Second: description of ulimit parameters

Limited does not limit the resources that users can use, but this setting applies to the maximum number of files that can be opened (max open files)

And the maximum number of processes that can run simultaneously (max user processes) is invalid

-a list all current resource limits

-c sets the maximum value of the core file. Unit: blocks

-d sets the maximum value of a process's data segment. Unit: kbytes

-f Shell the maximum file size of the created file (in blocks)

-h specifies that the hard limit of a given resource is set. If the user has root user rights, you can increase the hard limit. Any user can reduce the hard limit

-l the maximum physical memory that can be locked

The maximum resident memory that can be used by-m, in kbytes

-n the maximum number of files that each process can open at the same time

-p sets the maximum value of the pipe in block,1block=512bytes

-s specifies the maximum value of the stack in kbytes

-S specifies that a soft limit is set for a given resource. The soft limit can be increased to the hard limit. If the-H and-S flags are not specified, the limit applies to both.

-t specifies the number of seconds used by each process, in seconds

-u maximum number of concurrent processes that can be run

-v maximum virtual memory that can be used by Shell, in kbytes

Each line of output consists of the name of the resource, (units, arguments to the ulimit command), and soft limits. Detailed explanation:

Parameter description

The maximum value for core file size core files is 100 blocks

The data segment of the data seg size process can be arbitrarily large

File size files can be arbitrarily large

Pending signals has up to 2047 signals to be processed

Max locked memory the maximum physical memory locked by a task is 32kB

Max memory size the maximum resident physical memory of a task

Open files can open up to 1024 files at the same time for a task.

The maximum space for pipe size pipes is 4096 bytes.

The maximum message queue for POSIX message queues POSIX is 819200 bytes

The maximum stack of a stack size process is 8192 bytes

CPU time used by the cpu time process

The maximum number of processes (including threads) opened by the current user of max user processes is 2047.

Virtual memory does not limit the maximum address space of a process.

There is no limit to the maximum number of files that can be locked by file locks

Three: operation

Below, I set the maximum number of processes for a linux user to 10000:

Ulimit-u 10240

For Java applications that need to make a lot of socket connections and keep them open

It is best to modify the number of files that can be opened per process by using ulimit-n xx, which defaults to 1024.

Ulimit-n 4096 increases the number of files that can be opened by each process to 4096, which defaults to 1024

Other important settings that are recommended to be set to unlimited (unlimited) are:

Segment length: ulimit-d unlimited

Maximum memory size: ulimit-m unlimited

Stack size: ulimit-s unlimited

CPU time: ulimit-t unlimited

Virtual memory: ulimit-v unlimited

Temporarily, for the duration of a shell session logged in through the ulimit command.

Permanently, by adding a corresponding ulimit statement to the file read by the login shell

That is, user resource files specific to shell, such as:

1) remove the limit on the maximum number of processes and the maximum number of files opened on the Linux system:

Vi / etc/security/limits.conf

Add the following line soft noproc 11000hard noproc 11000soft nofile 4100hard nofile 4100

Note: * for all users, noproc represents the maximum number of processes, and nofile represents the maximum number of file openings

2) Let SSH accept the login of Login program, and it is convenient to view the ulimit-a resource limit in the ssh client:

A 、 vi / etc/ssh/sshd_config

Change the value of UserLogin to yes and remove the # comment

B. Restart the sshd service:

/ etc/init.d/sshd restart

3) modify the environment variable files of all linux users:

Vi / etc/profile

Ulimit-u 10000

Ulimit-n 4096

Ulimit-d unlimited

Ulimit-m unlimited

Ulimit-s unlimited

Ulimit-t unlimited

Ulimit-v unlimited

After saving, run # source / etc/profile to make it effective

Four: pay attention

Add the ulimit value to the / etc/profile file (for systems logged in with root privileges)

When configuring

To get a larger ulimit value each time the system restarts, add ulimit to the bottom of the / etc/profile file.

Echo ulimit-n 65535 > > / etc/profile

Source / etc/profile # load modified profile

In production, when you log in again when you are not a root user, your ulimint value does not change.

Solution:

Modify the software and hardware limitation file of linux / etc/security/limits.conf.

[root@hadoop001 security] # pwd

/ etc/security

[root@hadoop001 security] # ll

Total 68

....

-rw-r--r--. 1 root root 2508 Oct 15 2017 limits.conf

....

Add the following code at the end of the file:

Soft noproc 11000

Hard noproc 11000

Soft nofile 4100

Hard nofile 4100

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