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'''NOTE: This page describes Linux <tt>rlimit</tt> support (an SVr4/BSD4.3/POSIX.1-2001 standard). vServers can also be managed using the Linux Control Group (<tt>cgroup</tt>) system, for information on Control Group based resource management, see [[util-vserver:Cgroups|util-vserver - Cgroups]].''' Most properties related to system resources, might it be the memory consumption, the number of processes or file-handles, qualify for imposing limits on them. The Linux kernel provides the getrlimit and setrlimit system calls to get and set resource limits ''per process''. Each resource has an associated soft and hard limit. The soft limit is the value that the kernel enforces for the corresponding resource. The hard limit acts as a ceiling for the soft limit: an unprivileged process may only set its soft limit to a value in the range from 0 up to the hard limit, and (irreversibly) lower its hard limit. A privileged process (one with the CAP_SYS_RESOURCE capability) may make arbitrary changes to either limit value. The Linux-VServer kernel extends this system to provide resource limits for ''whole contexts'', not just single processes. Additionally a few new limit types missing in the vanilla kernel were introduced. Additionally the context limit system keeps track of observed maxima and resource limit hits, to provide some feedback for the administrator. See [[Context Accounting]] for details. __FORCETOC__ == List of Resource Limits == Below is a list of resource limits used for contexts and processes within. The tables contain the following information: ; ID : Resource limit ID ; Name : Human readable identifier used in userspace utilities ; procfs : Name used in /proc/virtual/*/limit ; ulimit : command line switch for the ulimit utility ; Unit : Aprropriate unit for the limit ; Tag : Special resource limit code to denote if resources are accounted, enforced (see below) ; Description : Description of capability/flag effects === Special Resource Limit Codes === The tag column may contain one or more of the following tags: {| class="wikitable_inline" ! Tag ! Description |- | A | Limit will be accounted |- | E | Limit will be enforced |} === Linux Resource Limits === Below is a list of resource limits available in vanilla Linux (>=2.6.18). {| class="wikitable_list" ! ID ! Name ! procfs ! ulimit ! Tag ! Unit ! Description |- | 0 | CPU | -- | -t | | ms | CPU time in ms |- | 1 | FSIZE | -- | -f | | KiB | Maximum file size |- | 2 | DATA | -- | -d | | KiB | Maximum size of the data segment |- | 3 | STACK | -- | -s | | KiB | Maximum stack size |- | 4 | CORE | -- | -c | | KiB | Maximum core file size |- | 5 | RSS | RSS | -m | AE | page | Maximum resident set size |- | 6 | NPROC | PROC | -u | AE | 1 | Maximum number of processes |- | 7 | NOFILE | FILES | -n | AE | 1 | Maximum number of open files |- | 8 | MEMLOCK | VML | -l | AE | page | Maximum locked-in-memory address space |- | 9 | AS | VM | -v | AE | page | Maximum address space size |- | 10 | LOCKS | LOCKS | -x | AE | 1 | Maximum file locks held |- | 11 | SIGPENDING | -- | -i | | 1 | Maximum number of pending signals |- | 12 | MSGQUEUE | MSGQ | -q | AE | Byte | Maximum bytes in POSIX mqueues |- | 13 | NICE | -- | | | 1 | Maximum nice prio allowed to raise to |- | 14 | RTPRIO | -- | -r | | 1 | Maximum realtime priority |} === Linux-VServer Resource Limits === Below is a list of additional resource limits available in the Linux-VServer kernel. {| class="wikitable_list" ! ID ! Name ! procfs ! Tag ! Unit ! Description |- | 16 | NSOCK | SOCK | AE | 1 | Maximum number of open sockets |- | 17 | OPENFD | OFD | AE | 1 | Maximum number of open file descriptors |- | 18 | ANON | ANON | A | page | Maximum anonymous memory size |- | 19 | SHMEM | SHM | AE | page | Maximum shared memory size |- | 20 | SEMARY | SEMA | A | 1 | Maximum number of semaphore arrays |- | 21 | NSEMS | SEMS | A | 1 | Maximum number of semaphores |- | 22 | DENTRY | DENT | AE | 1 | Maximum number of dentry structs |} == Determining the Page Size == You can use the following program to determine the page size for your architecture (if it supports the getpagesize() function) <pre> #include <stdlib.h> #include <stdint.h> #include <unistd.h> int main(int argc, char *argv[]) { int page_size = getpagesize(); printf("The page size is %d\n", page_size); exit(0); } </pre> Here's how to compile and run it (assuming you save it as pagesize.c): <pre> # gcc pagesize.c -o pagesize # ./pagesize The page size is 4096 </pre> '''Note''': Whether getpagesize() is present as a Linux system call depends on the architecture. If it is, it returns the kernel symbol PAGE_SIZE, which is architecture and machine model dependent. Generally, one uses binaries that are architecture but not machine model dependent, in order to have a single binary distribution per architecture. This means that a user program should not find PAGE_SIZE at compile time from a header file, but use an actual system call, at least for those architectures (like sun4) where this dependency exists. Here libc4, libc5, glibc 2.0 fail because their getpagesize() returns a statically derived value, and does not use a system call. Things are OK in glibc 2.1. If you prefer, you can get the pagesize using python, just start a python console and write: <pre> >>> import resource >>> resource.getpagesize() 4096 </pre> Most Linux operating systems also just support a simple native command <pre> getconf PAGESIZE </pre> Here are some typical page sizes ... {| class="wikitable_list" ! arch ! pagesize |- | arm, extensa, s390, sh64, x86, x86_64, v850 | 4k |- | alpha, cris | 8k |- | m68k, sparc | 4k, 8k |- | powerpc | 4k, 64k |- | parisc | 4k, 16k, 64k |- | ia64, mips | 4k, 8k, 16k, 64k |} == Configure Resource Limits in util-vserver == For example, if the adress space size (AS) and the resident set size (RSS) should be limited, the appropriate config files should be the following. You might have to create parent directories first. <pre> # ls -al /etc/vservers/myguest/rlimits total 28 drwxr-xr-x 2 root root 4096 2005-08-24 12:37 . drwxr-xr-x 5 root root 4096 2005-08-24 00:22 .. -rw-r--r-- 1 root root 6 2005-08-24 12:43 as -rw-r--r-- 1 root root 6 2005-08-24 12:37 rss # cat /etc/vservers/myguest/rlimits/as 90000 # cat /etc/vservers/myguest/rlimits/rss 10000 </pre> [[Category:Documentation]]
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