Resource Limits Unix (ulimit): The concept of resource limiting in Unix defines the way resources are set for a process. These resources are allocated for every user by the root or super user. We know that resources basically mean the memory,clock speed,time and stack for a process. It is important to note that the resources are set per user but they apply to per process. To wave off the fog of confusion consider this example.
Consider a web server of 16G memory which provides memory resources to all the process its sub users handle. Take a user “joe” who is allocated 8G of memory. If the user runs a process of 8G the server provides the required memory as the size can be complied by the server. The user runs another process simultaneously which requires a memory resource say 10 GB. Though the second process surpasses the memory deemed for the user , the process continues.
- 1 Ulimit command are used with various options and are as follows (for the lazier ones I have made it crisp)
- 2 Create file systems with large file support ulimit
Resource Limits Unix on ulimit command
On UNIX systems, the ulimit command controls the limits on system resource, such as process data size, process virtual memory, and process file size. Specifically:
- On Solaris systems, by default, the root user has unlimited access to these resources (for example, unlimited).
- On AIX, some limits might apply to the root user.
However there occurs a lag due to the overwhelming process size leading affecting the clock cycle. This allows parallel processing at the cost of CPU delay. Resource limiting is implemented using ulimit command. The ulimit command allows manipulation of data size, stack size, process virtual memory and process file size etc.
Solaris systems provide unlimited memory access to the root user by default. Other AIX systems lay certain limitations to the root user.
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- Resource limits on UNIX systems (ulimit)
Ulimit command are used with various options and are as follows (for the lazier ones I have made it crisp)
#ulimit -Ha Displays <strong>hard source limits.</strong>
#ulimit -Sa displays <strong>soft source limits.</strong>
#ulimit -d displays <strong>data memory
</strong>#ulimit -m displays <strong>virtual memory size</strong>
Here the hard source limits mean the the highest limit or the upper bound you can set for the user. The soft source limits give the lower limit for the resource. The soft source cannot be higher than the hard source limit.
<strong>gives unlimited resources to the data and virtual memory</strong>
#ulimit -f <strong>increases file size limit
fsize -1 <strong>gives unlimited access to the file size</strong>
Create file systems with large file support ulimit
The standard file system on AIX has a 2 GB file size limit, regardless of the ulimit setting. One way to enable files larger than the 2 GB limit is to create the file system with the Large File Enabled option. This option can be found through the Add a Journaled File System option of the smit menu. Refer to here to enable this option.
Edit/Change the Ulimit Values for uid:
- Edit the limits file under /etc/security/limits (takes effect after reboot)
- Use the chuser command to change individual user settings (logout and login required)
chuser fsize=-1 username
chuser data=-1 username
chuser nofiles=4000 username
chuser “stack=8388608? username