# Process limits

Limits are a per-process resource enforcement mechanism. This system provides a rudimentary backstop against runaway processes. cgroup is intended for account-wide resource limits.

Process limits are applied using a PAM wrapper on PAM-aware applications, which include any login service (FTP, mail, SSH, crond).

# Format

Limits may be overridden in Bootstrapper or by including a lexicographically higher file than 10-apnscp-system.conf (opens new window) in FST/siteinfo/etc/security/limits.d (see Filesystem.md. Files published within this location are inherited by all sites.

Settings take the following form:

# Disable coredumps for everyone
*         -    core     0
# Enable coredumps for users under "site12"
@foobar  soft core     unlimited
# Restrict number of files opened by PHP-FPM
nobody    soft nfiles   2048
# Limit any account with a user "phil" from running more than 25 processes
phil      hard nproc    25

Domain resolution

User resolution is completed inside the virtual environment. In the above example "phil" applies to any account with a user named "phil". Often it is inappropriate to publish limits within the FST except as stopgap limits for runaway resource consumption for all users (*) or the unprivileged PHP-FPM user, apache.

A domain may be of the form:

  • username, resolved within the vfs.
  • group name using @group syntax
  • wildcard * for default entry
  • wildcard %, can be also used with %group syntax, for maxlogin limit

# Resources

The following table summarizes available resource limits.

Value Units Remarks
core KB† Limits core file size. 0 disables core files.
data KB† Maximum data segment size.
fsize KB† Maximum filesize.
memlock KB Maximum locked-in-memory address space.
nofile [0,2^20]† Maximum number of open file descriptors.
rss KB† Ignored.
stack KB Maximum stack size.
cpu minutes Maximum CPU time.
nproc [0,2^63) Max number of processes.
as KB† Address space limit (vmem).
maxlogins Max number of logins for this user.
maxsyslogins Max number of global logins for system.
priority [0,2^63) Real-time process priority.
locks [0,2^63)† Max number of locks.
sigpending [0,2^63) Max number of pending signals.
msgqueue B Max memory used by POSIX message queues.
nice [-20, 19] Max nice priority allowed to raise.
rtprio [0,2^63) Max real-time priority.

values specified accept unlimited as a value.

# Hard and soft

Type may either be "hard" or "soft". A hard limit is the maximal value allowed for a resource. Only root may change this. Soft values may be changed by a user up to the hard limit.

Consider the following in site1/fst/etc/security/limits.d/nice-limit.conf:

* soft nice 0
* hard nice -5
su site1
# Reports admin
renice 0 $$
# 30307 (process ID) old priority 19, new priority 0
renice -1 $$
# renice: failed to set priority for 30307 (process ID): permission denied


A user is able to increase process priority from 19 down to 0 but may not specify a negative process priority, which preempts other processes on the system. A priority of 0 gives equal weighting to all system processes while a value greater than 0 would deprioritize.