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#include <sys/param.h>
#include <sys/sysctl.h>
| ctx | |
| Pointer to sysctl context or NULL, if no context. See sysctl_ctx_init(9) for how to create a new sysctl context. Programmers are strongly advised to use contexts to organize the dynamic OIDs which they create because when a context is destroyed all belonging sysctls are destroyed as well. This makes the sysctl cleanup code much simpler. Else deletion of all created OIDs is required at module unload. | |
| parent | |
| A pointer to a struct sysctl_oid_list, which is the head of the parent's list of children. This pointer is retrieved using the SYSCTL_STATIC_CHILDREN() macro for static sysctls and the SYSCTL_CHILDREN() macro for dynamic sysctls. The SYSCTL_PARENT() macro can be used to get the parent of an OID. The macro returns NULL if there is no parent. | |
| number | |
| The OID number that will be assigned to this OID. In almost all cases this should be set to OID_AUTO, which will result in the assignment of the next available OID number. | |
| name | |
| The name of the OID. The newly created OID will contain a copy of the name. | |
| ctlflags | |
| A bit mask of sysctl control flags. See the section below describing all the control flags. | |
| arg1 | |
| First callback argument for procedure sysctls. | |
| arg2 | |
| Second callback argument for procedure sysctls. | |
| len | |
| The length of the data pointed to by the ptr argument. For string type OIDs a length of zero means that strlen(3) will be used to get the length of the string at each access to the OID. For array type OIDs the length must be greater than zero. | |
| ptr | |
| Pointer to sysctl variable or string data. For sysctl values the pointer can be SYSCTL_NULL_XXX_PTR which means the OID is read-only and the returned value should be taken from the val argument. | |
| val | |
| If the ptr argument is SYSCTL_NULL_XXX_PTR, gives the constant value returned by this OID. Else this argument is not used. | |
| struct_type | |
| Name of structure type. | |
| handler | |
| A pointer to the function that is responsible for handling read and write requests to this OID. There are several standard handlers that support operations on nodes, integers, strings and opaque objects. It is possible to define custom handlers using the SYSCTL_PROC() macro or the SYSCTL_ADD_PROC() function. | |
| format | |
|
A pointer to a string
which specifies the format of the OID in a symbolic way.
This format is used as a hint by
sysctl(8)
to apply proper data formatting for display purposes.
Current formats: | |
| N | node |
| A | char * |
| I | int |
| IK[n] | temperature in Kelvin, multiplied by an optional single digit power of ten scaling factor: 1 (default) gives deciKelvin, 0 gives Kelvin, 3 gives milliKelvin |
| IU | unsigned int |
| L | long |
| LU | unsigned long |
| Q | quad_t |
| QU | u_quad_t |
| S,TYPE | struct TYPE structures |
| descr | |
| A pointer to a textual description of the OID. | |
| label | |
|
A pointer to an aggregation label for this component of the OID.
To make it easier to export sysctl data to monitoring systems that
support aggregations through labels (e.g., Prometheus),
this argument can be used to attach a label name to an OID.
The label acts as a hint that this component's name should not be part
of the metric's name,
but attached to the metric as a label instead.
Labels should only be applied to siblings that are structurally similar and encode the same type of value, as aggregation is of no use otherwise. | |
The sysctl_msec_to_ticks() handler can be used with SYSCTL_PROC() or SYSCTL_ADD_PROC() to export a millisecond time interval. When using this handler, the arg2 parameter points to an in-kernel variable of type int which stores a tick count suitable for use with functions like tsleep(9). The sysctl_msec_to_ticks() function converts this value to milliseconds when reporting the node's value. Similarly, sysctl_msec_to_ticks() accepts new values in milliseconds and stores an equivalent value in ticks to *arg2. Note that new code should use kernel variables of type sbintime_t instead of tick counts.
The SYSCTL_ADD_SBINTIME_MSEC() and SYSCTL_ADD_SBINTIME_USEC() functions and SYSCTL_SBINTIME_MSEC() and SYSCTL_SBINTIME_USEC() macros all create nodes which export an in-kernel variable of type sbintime_t. These nodes do not export the raw value of the associated variable. Instead, they export a 64-bit integer containing a count of either milliseconds (the MSEC variants) or microseconds (the USEC variants).
The SYSCTL_ADD_TIMEVAL_SEC() function and SYSCTL_TIMEVAL_SEC() macro create nodes which export an in-kernel variable of type struct timeval. These nodes do not export full value of the associated structure. Instead, they export a count in seconds as a simple integer which is stored in the tv_sec field of the associated variable. This function and macro are intended to be used with variables which store a non-negative interval rather than an absolute time. As a result, they reject attempts to store negative values.
| CTLTYPE_NODE | This is a node intended to be a parent for other nodes. |
| CTLTYPE_INT | This is a signed integer. |
| CTLTYPE_STRING | This is a nul-terminated string stored in a character array. |
| CTLTYPE_S8 | This is an 8-bit signed integer. |
| CTLTYPE_S16 | This is a 16-bit signed integer. |
| CTLTYPE_S32 | This is a 32-bit signed integer. |
| CTLTYPE_S64 | This is a 64-bit signed integer. |
| CTLTYPE_OPAQUE | This is an opaque data structure. |
| CTLTYPE_STRUCT | Alias for CTLTYPE_OPAQUE. |
| CTLTYPE_U8 | This is an 8-bit unsigned integer. |
| CTLTYPE_U16 | This is a 16-bit unsigned integer. |
| CTLTYPE_U32 | This is a 32-bit unsigned integer. |
| CTLTYPE_U64 | This is a 64-bit unsigned integer. |
| CTLTYPE_UINT | This is an unsigned integer. |
| CTLTYPE_LONG | This is a signed long. |
| CTLTYPE_ULONG | This is an unsigned long. |
All sysctl types except for new node declarations require one of the following flags to be set indicating the read and write disposition of the sysctl:
| CTLFLAG_RD | This is a read-only sysctl. |
| CTLFLAG_RDTUN | This is a read-only sysctl and tunable which is tried fetched once from the system environment early during module load or system boot. |
| CTLFLAG_WR | This is a writable sysctl. |
| CTLFLAG_RW | This sysctl is readable and writable. |
| CTLFLAG_RWTUN | This is a readable and writeable sysctl and tunable which is tried fetched once from the system environment early during module load or system boot. |
| CTLFLAG_NOFETCH | |
| In case the node is marked as a tunable using the CTLFLAG_[XX]TUN, this flag will prevent fetching the initial value from the system environment. Typically this flag should only be used for very early low level system setup code, and not by common drivers and modules. | |
| CTLFLAG_MPSAFE | This sysctl(9) handler is MP safe. Do not grab Giant around calls to this handler. This should only be used for SYSCTL_PROC() entries. |
Additionally, any of the following optional flags may also be specified:
| CTLFLAG_ANYBODY | |
| Any user or process can write to this sysctl. | |
| CTLFLAG_CAPRD | A process in capability mode can read from this sysctl. |
| CTLFLAG_CAPWR | A process in capability mode can write to this sysctl. |
| CTLFLAG_SECURE | This sysctl can be written to only if the effective securelevel of the process is [<=] 0. |
| CTLFLAG_PRISON | This sysctl can be written to by processes in jail(2). |
| CTLFLAG_SKIP | When iterating the sysctl name space, do not list this sysctl. |
| CTLFLAG_TUN | Advisory flag that a system tunable also exists for this variable. The initial sysctl value is tried fetched once from the system environment early during module load or system boot. |
| CTLFLAG_DYN | Dynamically created OIDs automatically get this flag set. |
| CTLFLAG_VNET | OID references a VIMAGE-enabled variable. |
SYSCTL_DECL(_security);
Examples of integer, opaque, string, and procedure sysctls follow:
/*
* Example of a constant integer value. Notice that the control
* flags are CTLFLAG_RD, the variable pointer is SYSCTL_NULL_INT_PTR,
* and the value is declared.
*/
SYSCTL_INT(_debug_sizeof, OID_AUTO, bio, CTLFLAG_RD, SYSCTL_NULL_INT_PTR,
sizeof(struct bio), "sizeof(struct bio)");
/*
* Example of a variable integer value. Notice that the control
* flags are CTLFLAG_RW, the variable pointer is set, and the
* value is 0.
*/
static int doingcache = 1; /* 1 => enable the cache */
SYSCTL_INT(_debug, OID_AUTO, vfscache, CTLFLAG_RW, &doingcache, 0,
"Enable name cache");
/*
* Example of a variable string value. Notice that the control
* flags are CTLFLAG_RW, that the variable pointer and string
* size are set. Unlike newer sysctls, this older sysctl uses a
* static oid number.
*/
char kernelname[MAXPATHLEN] = "/kernel"; /* XXX bloat */
SYSCTL_STRING(_kern, KERN_BOOTFILE, bootfile, CTLFLAG_RW,
kernelname, sizeof(kernelname), "Name of kernel file booted");
/*
* Example of an opaque data type exported by sysctl. Notice that
* the variable pointer and size are provided, as well as a format
* string for sysctl(8).
*/
static l_fp pps_freq; /* scaled frequency offset (ns/s) */
SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
&pps_freq, sizeof(pps_freq), "I", "");
/*
* Example of a procedure based sysctl exporting string
* information. Notice that the data type is declared, the NULL
* variable pointer and 0 size, the function pointer, and the
* format string for sysctl(8).
*/
SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING |
CTLFLAG_RW, NULL, 0, sysctl_kern_timecounter_hardware, "A",
"");
The following is an example of how to create a new top-level category and how to hook up another subtree to an existing static node. This example does not use contexts, which results in tedious management of all intermediate oids, as they need to be freed later on:
#include <sys/sysctl.h> ... /* * Need to preserve pointers to newly created subtrees, * to be able to free them later: */ static struct sysctl_oid *root1; static struct sysctl_oid *root2; static struct sysctl_oid *oidp; static int a_int; static char *string = "dynamic sysctl"; ...root1 = SYSCTL_ADD_ROOT_NODE(NULL, OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree"); oidp = SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(root1), OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf"); ... root2 = SYSCTL_ADD_NODE(NULL, SYSCTL_STATIC_CHILDREN(_debug), OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug"); oidp = SYSCTL_ADD_STRING(NULL, SYSCTL_CHILDREN(root2), OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf");
This example creates the following subtrees:
debug.newtree.newstring newtree.newint
Care should be taken to free all OIDs once they are no longer needed!
The semantics chosen for a new sysctl should be as clear as possible, and the name of the sysctl must closely reflect its semantics. Therefore the sysctl name deserves a fair amount of consideration. It should be short but yet representative of the sysctl meaning. If the name consists of several words, they should be separated by underscore characters, as in compute_summary_at_mount. Underscore characters may be omitted only if the name consists of not more than two words, each being not longer than four characters, as in bootfile.
For boolean sysctls, negative logic should be totally avoided. That is, do not use names like no_foobar or foobar_disable. They are confusing and lead to configuration errors. Use positive logic instead: foobar, foobar_enable.
A temporary sysctl node OID that should not be relied upon must be designated as such by a leading underscore character in its name. For example: _dirty_hack.
This man page was written by Robert N. M. Watson.
The following top level sysctl name spaces are commonly used:
| compat | |
| Compatibility layer information. | |
| debug | |
| Debugging information. Various name spaces exist under debug. | |
| hw | |
| Hardware and device driver information. | |
| kern | |
| Kernel behavior tuning; generally deprecated in favor of more specific name spaces. | |
| machdep | |
| Machine-dependent configuration parameters. | |
| net | |
| Network subsystem. Various protocols have name spaces under net. | |
| regression | |
| Regression test configuration and information. | |
| security | |
| Security and security-policy configuration and information. | |
| sysctl | |
| Reserved name space for the implementation of sysctl. | |
| user | |
| Configuration settings relating to user application behavior. Generally, configuring applications using kernel sysctls is discouraged. | |
| vfs | |
| Virtual file system configuration and information. | |
| vm | |
| Virtual memory subsystem configuration and information. | |
| SYSCTL (9) | September 1, 2020 |
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