You need to use the sysctl command which is used to modify kernel parameters at runtime. The parameters available are those listed under /proc/sys/. Procfs is required for sysctl support in Linux. You can use sysctl command to both read and write sysctl variables.
You must login as the root user to use any one of the following command on a Linux operating systems.
Display Linux kernel parameters
The syntax is:
# sysctl variable
####################################
### Display all sysctl variables ###
####################################
# sysctl -a
# sysctl -a | more
# sysctl -a | grep 'something'
# sysctl -a | grep memory
Sample outputs:
vm.memory_failure_early_kill = 0 vm.memory_failure_recovery = 1 vm.overcommit_memory = 0
To see value for kernel variable called kernel.hostname, enter:
# sysctl -n kernel.hostname
How do I set new values?
There are three methods to set new values for given kernel parameters as follows:
Method # 1: Setting value via procfs
You can use standard echo command to write data to variables (this temporary change):
# echo "value" > /proc/sys/location/variable
Method # 2: Temporary on the command line
Use sysctl command with -w option when you want to change a sysctl setting:
sysctl -w variable=value
Method # 3: Configuration file /etc/sysctl.conf
This is recommended way. First open /etc/sysctl.conf file, enter:
# vi /etc/sysctl.conf
Now add value:
variable = value
Close and save the changes. Type the following command to load sysctl settings from the file /etc/sysctl.conf file:
# sysctl -p
OR
# sysctl -p /etc/sysctl.conf
The last method will load settings permanently at boot time from /etc/sysctl.conf file. Read man page of sysctl for information:
$ man sysctl
2 comment
Can you make an example for “variable” and “value” ?
EXAMPLE….
[root@hostname1 /]# sysctl -a
kernel.sched_child_runs_first = 0
kernel.sched_min_granularity_ns = 4000000
kernel.sched_latency_ns = 20000000
kernel.sched_wakeup_granularity_ns = 4000000
kernel.sched_tunable_scaling = 1
kernel.sched_features = 3183
kernel.sched_migration_cost = 500000
kernel.sched_nr_migrate = 32
kernel.sched_time_avg = 1000
kernel.sched_shares_window = 10000000
kernel.timer_migration = 1
kernel.sched_rt_period_us = 1000000
kernel.sched_rt_runtime_us = 950000
kernel.sched_compat_yield = 0
kernel.sched_rr_timeslice_ms = 100
kernel.sched_autogroup_enabled = 0
kernel.sched_cfs_bandwidth_slice_us = 5000
kernel.panic = 0
kernel.exec-shield = 1
kernel.core_uses_pid = 1
kernel.core_pattern = |/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t e
kernel.core_pipe_limit = 4
kernel.tainted = 0
kernel.real-root-dev = 0
kernel.print-fatal-signals = 0
kernel.ctrl-alt-del = 0
kernel.ftrace_enabled = 1
kernel.stack_tracer_enabled = 0
kernel.ftrace_dump_on_oops = 0
kernel.modprobe = /sbin/modprobe
kernel.modules_disabled = 0
kernel.kexec_load_disabled = 0
kernel.hotplug =
kernel.acct = 4 2 30
kernel.sysrq = 0
kernel.cad_pid = 1
kernel.threads-max = 513406
kernel.random.poolsize = 4096
kernel.random.entropy_avail = 135
kernel.random.read_wakeup_threshold = 64
kernel.random.write_wakeup_threshold = 128
kernel.random.boot_id = 95a40261-6816-445f-b5ae-38660f15d7e3
kernel.random.uuid = 7a1d1848-0868-42f5-bb3b-21172b60996b
kernel.usermodehelper.bset = 4294967295 4294967295
kernel.usermodehelper.inheritable = 4294967295 4294967295
kernel.overflowuid = 65534
kernel.overflowgid = 65534
kernel.pid_max = 32768
kernel.panic_on_oops = 1
kernel.printk = 4 4 1 7
kernel.printk_ratelimit = 5
kernel.printk_ratelimit_burst = 10
kernel.printk_delay = 0
kernel.dmesg_restrict = 0
kernel.kptr_restrict = 1
kernel.ngroups_max = 65536
kernel.watchdog = 1
kernel.watchdog_thresh = 60
kernel.softlockup_panic = 0
kernel.nmi_watchdog = 1
kernel.unknown_nmi_panic = 0
kernel.panic_on_unrecovered_nmi = 0
kernel.panic_on_io_nmi = 0
kernel.bootloader_type = 113
kernel.bootloader_version = 1
kernel.kstack_depth_to_print = 12
kernel.io_delay_type = 0
kernel.randomize_va_space = 2
kernel.acpi_video_flags = 0
kernel.hung_task_panic = 0
kernel.hung_task_check_count = 4194304
kernel.hung_task_timeout_secs = 120
kernel.hung_task_warnings = 10
kernel.compat-log = 1
kernel.max_lock_depth = 1024
kernel.poweroff_cmd = /sbin/poweroff
kernel.keys.maxkeys = 200
kernel.keys.maxbytes = 20000
kernel.keys.root_maxkeys = 1000000
kernel.keys.root_maxbytes = 25000000
kernel.keys.gc_delay = 300
kernel.slow-work.min-threads = 2
kernel.slow-work.max-threads = 8
kernel.slow-work.vslow-percentage = 50
kernel.perf_event_paranoid = 1
kernel.perf_event_mlock_kb = 516
kernel.perf_event_max_sample_rate = 100000
(VARIABLE = VALUE)
sysctl -w variable=value
sysctl -w kernel.keys.maxkeys=400