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115 lines
3.0 KiB
ReStructuredText
115 lines
3.0 KiB
ReStructuredText
.. _resource-limits:
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Resource limits
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###############
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Linux systems employ limiting or quota mechanisms to provide quality of
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service for system resources and contain rogue processes.
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These limits are layered at the system-level and user-level. If these limits
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need to be modified, it is useful to understand the different limit
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configurations.
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.. contents:: :local:
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:depth: 2
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System-wide limits
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==================
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Some global resource limits are implemented in the Linux kernel and are
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controllable with kernel parameters.
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For example, a global limit for the maximum number of open files is set with
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the *fs.file-max* parameter. This limit applies to all processes and users an
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cannot be exceeded other limit values.
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Checking limit
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**************
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You can check a current value with :command:`sysctl -n <PARAMETER>`. For
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example:
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.. code:: bash
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sysctl -n fs.file-max
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This *fs.file-max* value is set intentionally high on |CL| systems by
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default. You can check the maximum value supported by the system with:
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.. code::
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cat /proc/sys/fs/file-max
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Overriding limit
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****************
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You can override a value with :command:`sysctl -w <PARAMETER>`. For
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example:
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.. code:: bash
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sudo sysctl -w fs.file-max=<NUMBER>
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If needed permanently, the value can be set by creating a
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:file:`/etc/sysctl.d/*.conf` file (see :command:`man sysctl.d` for details).
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For example:
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.. code:: bash
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sudo mkdir -p /etc/sysctl.d/
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sudo tee /etc/sysctl.d/fs-file-max.conf > /dev/null <<'EOF'
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fs.file-max=<NUMBER>
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EOF
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Per-user limits
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===============
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For processes not managed by systemd, resource limits can be set for PAM
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logins on a per-user basis with upper and lower limits in the
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:file:`/etc/security/limits.conf` file.
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You can set temporary values and check the current values with the
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:command:`ulimit` command. For example, to change the soft limit of maximum
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number of open file descriptors for the current user:
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.. code::
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ulimit -S -n <NUMBER>
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See :command:`man limits.conf` for details.
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Service limits
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==============
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Resource limits for services started with systemd units do not follow normal
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user limits because the process is started in a separate `Linux control group
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(cgroup) <https://www.kernel.org/doc/Documentation/cgroup-v2.txt>`_ Linux
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cgroups associate related process groups and provide resource accounting.
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Resource limits for individual systemd services can be controlled inside their
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unit files or its configuration drop-in directory with the resource Limit
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directives. See `process properties section of the systemd.exec man page
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<https://www.freedesktop.org/software/systemd/man/systemd.exec.html>`_.
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Resource limits for all systemd services can be controlled with a file in the
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:file:`/etc/systemd/system.conf.d/` directory. For example, to have no
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restriction on the number of open files:
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.. code::
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sudo mkdir -p /etc/systemd/system.conf.d/
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sudo tee /etc/systemd/system.conf.d/50-nfiles.conf > /dev/null <<'EOF'
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[Manager]
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DefaultLimitNOFILE=infinity
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EOF
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