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@(#)1.7.t 8.4 (Berkeley) 5/26/94
.Sh 2 "System operation support
Unless noted otherwise, the calls in this section are permitted only to a privileged user. .Sh 3 "Monitoring system operation
The .Fn sysctl function allows any process to retrieve system information and allows processes with appropriate privileges to set system configurations. .Fd sysctl 6 "get or set system information sysctl(name, namelen, oldp, oldlenp, newp, newlen); int *name; u_int namelen; result void *oldp; result size_t *oldlenp; void *newp; size_t newlen; The information available from .Fn sysctl consists of integers, strings, and tables. .Fn Sysctl returns a consistent snapshot of the data requested. Consistency is obtained by locking the destination buffer into memory so that the data may be copied out without blocking. Calls to .Fn sysctl are serialized to avoid deadlock.
The object to be interrogated or set is named using a ``Management Information Base'' (MIB) style name, listed in name, which is a namelen length array of integers. This name is from a hierarchical name space, with the most significant component in the first element of the array. It is analogous to a file pathname, but with integers as components rather than slash-separated strings.
The information is copied into the buffer specified by oldp. The size of the buffer is given by the location specified by oldlenp before the call, and that location is filled in with the amount of data copied after a successful call. If the amount of data available is greater than the size of the buffer supplied, the call supplies as much data as fits in the buffer provided and returns an error.
To set a new value, newp is set to point to a buffer of length newlen from which the requested value is to be taken. If a new value is not to be set, newp should be set to NULL and newlen set to 0.
The top level names (those used in the first element of the name array) are defined with a CTL_ prefix in <sys/sysctl.h>, and are as follows. The next and subsequent levels down are found in the include files listed here:
| Name Next Level Names Description |
| CTL\_DEBUG sys/sysctl.h Debugging |
| CTL\_FS sys/sysctl.h Filesystem |
| CTL\_HW sys/sysctl.h Generic CPU, I/O |
| CTL\_KERN sys/sysctl.h High kernel limits |
| CTL\_MACHDEP sys/sysctl.h Machine dependent |
| CTL\_NET sys/socket.h Networking |
| CTL\_USER sys/sysctl.h User-level |
| CTL\_VM vm/vm_param.h Virtual memory |
The call: .Fd mount 4 "mount a filesystem mount(type, dir, flags, data); int type; char *dir; int flags; caddr_t data; extends the name space. The .Fn mount call grafts a filesystem object onto the system file tree at the point specified in dir. The argument type specifies the type of filesystem to be mounted. The argument data describes the filesystem object to be mounted according to the type. The contents of the filesystem become available through the new mount point dir. Any files in or below dir at the time of a successful mount disappear from the name space until the filesystem is unmounted. The flags value specifies generic properties, such as a request to mount the filesystem read-only.
Information about all mounted filesystems can be obtained with the call: .Fd getfsstat 3 "get list of all mounted filesystems getfsstat(buf, bufsize, flags); result struct statfs *buf; long bufsize, int flags;
The call: .Fd swapon 1 "add a swap device for interleaved paging/swapping swapon(blkdev); char *blkdev; specifies a device to be made available for paging and swapping. .Sh 3 "Shutdown operations
The call: .Fd unmount 2 "dismount a filesystem unmount(dir, flags); char *dir; int flags; unmounts the filesystem mounted on dir. This call will succeed only if the filesystem is not currently being used or if the MNT_FORCE flag is specified.
The call: .Fd sync 0 "force completion of pending disk writes (flush cache) sync(); schedules I/O to flush all modified disk blocks resident in the kernel. (This call does not require privileged status.) Files can be selectively flushed to disk using the .Fn fsync call (see section .Xr 2.2.6 ).
The call: .Fd reboot 1 "reboot system or halt processor reboot(how); int how; causes a machine halt or reboot. The call may request a reboot by specifying how as RB_AUTOBOOT, or that the machine be halted with RB_HALT, among other options. These constants are defined in <sys/reboot.h>. .Sh 3 "Accounting
The system optionally keeps an accounting record in a file for each process that exits on the system. The format of this record is beyond the scope of this document. The accounting may be enabled to a file name by doing: .Fd acct 1 "enable or disable process accounting acct(path); char *path; If path is NULL, then accounting is disabled. Otherwise, the named file becomes the accounting file.