ulimit: difference between hard and soft limitsLimits on the number of file descriptorsulimit & rlimit in Linux, are they the same thing?ulimit vs. limit on FreeBSD 8.3Limits on the number of file descriptorsWhat are the effects of increasing hard and soft limits for ldap userProcess specific ulimit still low after changes to soft and hard ulimitsHow “Max open files” soft and hard limit are set for specific process?Configuring ulimit of `max open files` for daemonized nginx master processSoft limit vs hard limitSetting OS X/MacOS/BSD maxfileulimit value not changing for a processIncreasing open files limit for all processes: Do I need to set Soft/Hard limits?Why ulimit -n modifies hard limit
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ulimit: difference between hard and soft limits
Limits on the number of file descriptorsulimit & rlimit in Linux, are they the same thing?ulimit vs. limit on FreeBSD 8.3Limits on the number of file descriptorsWhat are the effects of increasing hard and soft limits for ldap userProcess specific ulimit still low after changes to soft and hard ulimitsHow “Max open files” soft and hard limit are set for specific process?Configuring ulimit of `max open files` for daemonized nginx master processSoft limit vs hard limitSetting OS X/MacOS/BSD maxfileulimit value not changing for a processIncreasing open files limit for all processes: Do I need to set Soft/Hard limits?Why ulimit -n modifies hard limit
What is the difference between hard and soft limits in ulimit?
For number of open files, I have a soft limit of 1024 and a hard limit of 10240.
It is possible to run programs opening more than 1024 files. What is the soft limit for?
open-files ulimit
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
add a comment |
What is the difference between hard and soft limits in ulimit?
For number of open files, I have a soft limit of 1024 and a hard limit of 10240.
It is possible to run programs opening more than 1024 files. What is the soft limit for?
open-files ulimit
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
4
Are you talking aboutulimit -n? Try running a shell with a very low value (bash -c 'ulimit -n 4; exec 3>a; exec 4>b; exec 5>c'). What's the output?
– Gilles
Jan 20 '12 at 17:23
add a comment |
What is the difference between hard and soft limits in ulimit?
For number of open files, I have a soft limit of 1024 and a hard limit of 10240.
It is possible to run programs opening more than 1024 files. What is the soft limit for?
open-files ulimit
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
What is the difference between hard and soft limits in ulimit?
For number of open files, I have a soft limit of 1024 and a hard limit of 10240.
It is possible to run programs opening more than 1024 files. What is the soft limit for?
open-files ulimit
open-files ulimit
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
edited Jan 20 '12 at 17:08
user13742
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
asked Jan 20 '12 at 16:59
daniel kullmanndaniel kullmann
5,28272842
5,28272842
4
Are you talking aboutulimit -n? Try running a shell with a very low value (bash -c 'ulimit -n 4; exec 3>a; exec 4>b; exec 5>c'). What's the output?
– Gilles
Jan 20 '12 at 17:23
add a comment |
4
Are you talking aboutulimit -n? Try running a shell with a very low value (bash -c 'ulimit -n 4; exec 3>a; exec 4>b; exec 5>c'). What's the output?
– Gilles
Jan 20 '12 at 17:23
4
4
Are you talking about
ulimit -n? Try running a shell with a very low value (bash -c 'ulimit -n 4; exec 3>a; exec 4>b; exec 5>c'). What's the output?– Gilles
Jan 20 '12 at 17:23
Are you talking about
ulimit -n? Try running a shell with a very low value (bash -c 'ulimit -n 4; exec 3>a; exec 4>b; exec 5>c'). What's the output?– Gilles
Jan 20 '12 at 17:23
add a comment |
2 Answers
2
active
oldest
votes
A hard limit can only be raised by root (any process can lower it). So it is useful for security: a non-root process cannot overstep a hard limit. But it's inconvenient in that a non-root process can't have a lower limit than its children.
A soft limit can be changed by the process at any time. So it's convenient as long as processes cooperate, but no good for security.
A typical use case for soft limits is to disable core dumps (ulimit -Sc 0) while keeping the option of enabling them for a specific process you're debugging ((ulimit -Sc unlimited; myprocess)).
The ulimit shell command is a wrapper around the setrlimit system call, so that's where you'll find the definitive documentation.
Note that some systems may not implement all limits. Specifically, some systems don't support per-process limits on file descriptors (Linux does); if yours doesn't, the shell command may be a no-op.
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
5
+1 for the soft limits use case. Resident set size limit (ulimit -m,RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v,RLIMIT_AS) works, though.
– Adam Zalcman
Jan 20 '12 at 17:53
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
1
@Ryan Yes, a program can change its own soft limit at any time by callingsetrlimit(to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue asetrlimitcall, or under Linux you can callprlimit(for which I don't know of any shell utility).
– Gilles
Jun 29 '13 at 8:27
There is now aprlimitshell utility too.
– telcoM
yesterday
add a comment |
The hard limit is for the security purpose. For a non-root user, he can only decrease the hard limit from the currently set hard limit; he cannot increase it. Increasing the hard limit can be done only by root user (or maybe with sudo privilege, not sure about that). What a non-root user can do is choose a limit (called soft limit) which can be in the range [0, hard limit] for its processes. Its the soft limit which is seen and taken in consideration by the processes.
answered yesterday
Ankit ShubhamAnkit Shubham
1112
add a comment |
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2 Answers
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active
oldest
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2 Answers
2
active
oldest
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oldest
votes
A hard limit can only be raised by root (any process can lower it). So it is useful for security: a non-root process cannot overstep a hard limit. But it's inconvenient in that a non-root process can't have a lower limit than its children.
A soft limit can be changed by the process at any time. So it's convenient as long as processes cooperate, but no good for security.
A typical use case for soft limits is to disable core dumps (ulimit -Sc 0) while keeping the option of enabling them for a specific process you're debugging ((ulimit -Sc unlimited; myprocess)).
The ulimit shell command is a wrapper around the setrlimit system call, so that's where you'll find the definitive documentation.
Note that some systems may not implement all limits. Specifically, some systems don't support per-process limits on file descriptors (Linux does); if yours doesn't, the shell command may be a no-op.
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
5
+1 for the soft limits use case. Resident set size limit (ulimit -m,RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v,RLIMIT_AS) works, though.
– Adam Zalcman
Jan 20 '12 at 17:53
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
1
@Ryan Yes, a program can change its own soft limit at any time by callingsetrlimit(to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue asetrlimitcall, or under Linux you can callprlimit(for which I don't know of any shell utility).
– Gilles
Jun 29 '13 at 8:27
There is now aprlimitshell utility too.
– telcoM
yesterday
add a comment |
A hard limit can only be raised by root (any process can lower it). So it is useful for security: a non-root process cannot overstep a hard limit. But it's inconvenient in that a non-root process can't have a lower limit than its children.
A soft limit can be changed by the process at any time. So it's convenient as long as processes cooperate, but no good for security.
A typical use case for soft limits is to disable core dumps (ulimit -Sc 0) while keeping the option of enabling them for a specific process you're debugging ((ulimit -Sc unlimited; myprocess)).
The ulimit shell command is a wrapper around the setrlimit system call, so that's where you'll find the definitive documentation.
Note that some systems may not implement all limits. Specifically, some systems don't support per-process limits on file descriptors (Linux does); if yours doesn't, the shell command may be a no-op.
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
5
+1 for the soft limits use case. Resident set size limit (ulimit -m,RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v,RLIMIT_AS) works, though.
– Adam Zalcman
Jan 20 '12 at 17:53
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
1
@Ryan Yes, a program can change its own soft limit at any time by callingsetrlimit(to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue asetrlimitcall, or under Linux you can callprlimit(for which I don't know of any shell utility).
– Gilles
Jun 29 '13 at 8:27
There is now aprlimitshell utility too.
– telcoM
yesterday
add a comment |
A hard limit can only be raised by root (any process can lower it). So it is useful for security: a non-root process cannot overstep a hard limit. But it's inconvenient in that a non-root process can't have a lower limit than its children.
A soft limit can be changed by the process at any time. So it's convenient as long as processes cooperate, but no good for security.
A typical use case for soft limits is to disable core dumps (ulimit -Sc 0) while keeping the option of enabling them for a specific process you're debugging ((ulimit -Sc unlimited; myprocess)).
The ulimit shell command is a wrapper around the setrlimit system call, so that's where you'll find the definitive documentation.
Note that some systems may not implement all limits. Specifically, some systems don't support per-process limits on file descriptors (Linux does); if yours doesn't, the shell command may be a no-op.
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
A hard limit can only be raised by root (any process can lower it). So it is useful for security: a non-root process cannot overstep a hard limit. But it's inconvenient in that a non-root process can't have a lower limit than its children.
A soft limit can be changed by the process at any time. So it's convenient as long as processes cooperate, but no good for security.
A typical use case for soft limits is to disable core dumps (ulimit -Sc 0) while keeping the option of enabling them for a specific process you're debugging ((ulimit -Sc unlimited; myprocess)).
The ulimit shell command is a wrapper around the setrlimit system call, so that's where you'll find the definitive documentation.
Note that some systems may not implement all limits. Specifically, some systems don't support per-process limits on file descriptors (Linux does); if yours doesn't, the shell command may be a no-op.
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
answered Jan 20 '12 at 17:17
GillesGilles
544k12811041621
544k12811041621
5
+1 for the soft limits use case. Resident set size limit (ulimit -m,RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v,RLIMIT_AS) works, though.
– Adam Zalcman
Jan 20 '12 at 17:53
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
1
@Ryan Yes, a program can change its own soft limit at any time by callingsetrlimit(to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue asetrlimitcall, or under Linux you can callprlimit(for which I don't know of any shell utility).
– Gilles
Jun 29 '13 at 8:27
There is now aprlimitshell utility too.
– telcoM
yesterday
add a comment |
5
+1 for the soft limits use case. Resident set size limit (ulimit -m,RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v,RLIMIT_AS) works, though.
– Adam Zalcman
Jan 20 '12 at 17:53
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
1
@Ryan Yes, a program can change its own soft limit at any time by callingsetrlimit(to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue asetrlimitcall, or under Linux you can callprlimit(for which I don't know of any shell utility).
– Gilles
Jun 29 '13 at 8:27
There is now aprlimitshell utility too.
– telcoM
yesterday
5
5
+1 for the soft limits use case. Resident set size limit (
ulimit -m, RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v, RLIMIT_AS) works, though.– Adam Zalcman
Jan 20 '12 at 17:53
+1 for the soft limits use case. Resident set size limit (
ulimit -m, RLIMIT_RSS) is an example of a limit that isn't effective on Linux anymore. Virtual memory limit (ulimit -v, RLIMIT_AS) works, though.– Adam Zalcman
Jan 20 '12 at 17:53
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
@Gilles, do you mean without restarting the process, when we change the soft limit, it can be effect immediately?
– Ryan
Jun 29 '13 at 2:52
1
1
@Ryan Yes, a program can change its own soft limit at any time by calling
setrlimit (to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue a setrlimit call, or under Linux you can call prlimit (for which I don't know of any shell utility).– Gilles
Jun 29 '13 at 8:27
@Ryan Yes, a program can change its own soft limit at any time by calling
setrlimit (to the extent permitted by the hard limit unless running as root of course). Most programs don't have a command that lets the user do that, but you can try attaching to the program with a debugger and making it issue a setrlimit call, or under Linux you can call prlimit (for which I don't know of any shell utility).– Gilles
Jun 29 '13 at 8:27
There is now a
prlimit shell utility too.– telcoM
yesterday
There is now a
prlimit shell utility too.– telcoM
yesterday
add a comment |
The hard limit is for the security purpose. For a non-root user, he can only decrease the hard limit from the currently set hard limit; he cannot increase it. Increasing the hard limit can be done only by root user (or maybe with sudo privilege, not sure about that). What a non-root user can do is choose a limit (called soft limit) which can be in the range [0, hard limit] for its processes. Its the soft limit which is seen and taken in consideration by the processes.
answered yesterday
Ankit ShubhamAnkit Shubham
1112
add a comment |
The hard limit is for the security purpose. For a non-root user, he can only decrease the hard limit from the currently set hard limit; he cannot increase it. Increasing the hard limit can be done only by root user (or maybe with sudo privilege, not sure about that). What a non-root user can do is choose a limit (called soft limit) which can be in the range [0, hard limit] for its processes. Its the soft limit which is seen and taken in consideration by the processes.
answered yesterday
Ankit ShubhamAnkit Shubham
1112
add a comment |
The hard limit is for the security purpose. For a non-root user, he can only decrease the hard limit from the currently set hard limit; he cannot increase it. Increasing the hard limit can be done only by root user (or maybe with sudo privilege, not sure about that). What a non-root user can do is choose a limit (called soft limit) which can be in the range [0, hard limit] for its processes. Its the soft limit which is seen and taken in consideration by the processes.
answered yesterday
Ankit ShubhamAnkit Shubham
1112
The hard limit is for the security purpose. For a non-root user, he can only decrease the hard limit from the currently set hard limit; he cannot increase it. Increasing the hard limit can be done only by root user (or maybe with sudo privilege, not sure about that). What a non-root user can do is choose a limit (called soft limit) which can be in the range [0, hard limit] for its processes. Its the soft limit which is seen and taken in consideration by the processes.
answered yesterday
Ankit ShubhamAnkit Shubham
1112
answered yesterday
Ankit ShubhamAnkit Shubham
1112
answered yesterday
Ankit ShubhamAnkit Shubham
1112
answered yesterday
Ankit ShubhamAnkit Shubham
1112
1112
add a comment |
add a comment |
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4
Are you talking about
ulimit -n? Try running a shell with a very low value (bash -c 'ulimit -n 4; exec 3>a; exec 4>b; exec 5>c'). What's the output?– Gilles
Jan 20 '12 at 17:23