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from: @(#)iostat.8 8.1 (Berkeley) 6/6/93
.Dd July 29, 2018 .Dt IOSTAT 8 .Os .Sh NAME .Nm iostat .Nd report I/O statistics .Sh SYNOPSIS .Nm .Op Fl CdDITxy .Op Fl c Ar count .Op Fl w Ar wait .Op Ar drives .Sh DESCRIPTION .Nm displays kernel I/O statistics on terminal, disk and CPU operations. By default, .Nm displays one line of statistics averaged over the machine's run time. The use of .Fl c presents successive lines averaged over the .Ar wait period. The .Fl I option causes .Nm to print raw, unaveraged values.
p Only the last disk option specified .Fl ( d , .Fl D , or .Fl x ) is used.
p The options are as follows: l -tag -width XNXsystemX t Fl c Ar count Repeat the display .Ar count times. Unless the .Fl I flag is in effect, the first display is for the time since a reboot and each subsequent report is for the time period since the last display. If no .Ar wait interval is specified, the default is 1 second. t Fl C Show CPU statistics. This is enabled by default unless the .Fl d , .Fl D , .Fl T , or .Fl x flags are used. t Fl d Show disk statistics. This is the default. Displays kilobytes per transfer, number of transfers, and megabytes transferred. Use of this flag disables display of CPU and tty statistics. t Fl D Show alternative disk statistics. Displays kilobytes transferred, number of transfers, and time spent in transfers. Use of this flag disables the default display. t Fl I Show the running total values, rather than an average. t Fl T Show tty statistics. This is enabled by default unless the .Fl C , .Fl d , or .Fl D flags are used. t Fl w Ar wait Pause .Ar wait seconds between each display. If no repeat .Ar count is specified, the default is infinity. t Fl x Show extended disk statistics. Each disk is displayed on a line of its own with all available statistics. This option overrides all other display options, and all disks are displayed unless specific disks are provided as arguments. Additionally, separate read and write statistics are displayed. t Fl y Shows the extended statistics and additional queuing statistics. .El
p .Nm displays its information in the following format: l -tag -width flag t tty l -tag -width indent -compact t tin characters read from terminals t tout characters written to terminals .El t disks Disk operations. The header of the field is the disk name and unit number. If more drives are configured in the system that fit across the current display, .Nm displays only those drives that fit on the display. To force .Nm to display specific drives, they may be supplied on the command line, either as names or .Fn fnmatch patterns.
p l -tag -width indent -compact t KB/t Kilobytes transferred per disk transfer t t/s transfers per second t MB/s Megabytes transferred per second .El The alternative display format, (selected with .Fl D ) , presents the following values. l -tag -width indent -compact t KB Kilobytes transferred t xfr Disk transfers t time Seconds spent in disk activity .El With the .Fl y flag, the following queuing measurements are added l -tag -width indent -compact t wait Number of I/O requests queued up t actv Number of currently active I/O requests t wsvc_t Average waiting time of an I/O request in milliseconds t asvc_t Average duration of an I/O request in milliseconds t wtime Seconds spent in the waiting queue. Queuing data might not be available from all drivers and is then shown as zeros. .El t cpu l -tag -width indent -compact t us % of CPU time in user mode t ni % of CPU time in user mode running niced processes t sy % of CPU time in system mode t in % of CPU time in interrupt mode t id % of CPU time in idle mode .El .El .Sh SEE ALSO .Xr fstat 1 , .Xr netstat 1 , .Xr nfsstat 1 , .Xr ps 1 , .Xr systat 1 , .Xr vmstat 1 , .Xr fnmatch 3 , .Xr pstat 8
p The sections starting with ``Interpreting system activity'' in .%T "Installing and Operating 4.3BSD" . .Sh HISTORY .Nm appeared in .At v6 . The .Fl x option was added in .Nx 1.4 . Collection of queueing values and the .Fl y option were added in .Nx 8.0 .
Indexes created Mon Oct 20 11:09:49 GMT 2025