User`s guide

Cryptography

• The value of the SCSI error-handling timeout is now tunable. If a SCSI device times out while processing

file system I/O, the kernel attempts to bring the device back online by resetting the device, followed by

resetting the bus, and finally by resetting the controller. The error-handling timeout defines how many

seconds the kernel should wait for a response after each recovery attempt before performing the next

step in the process. For some fast-fail scenarios, it is useful to be able to adjust this value as the kernel

might need additional time to try several combinations of bus device, target, bus, and controller. You

can read and set the timeout via /sys/class/scsi_device/*/device/eh_timeout. The default

timeout value is 10 seconds. (3.8)

• Variable-sized huge pages via the flags argument to mmap() or the shmflg argument to shmget().

Bits 26-31 of these arguments specify the base-2 logarithm of the page size. For example, values of 21

<< 26 and 30 << 26 represent page sizes of 2 MB (2^21) and 1 GB (2^30) respectively. A value of

zero selects the default huge page size. (3.8)

• The watchdog timer device (displayed in /proc/devices) provides a framework for all watchdog timer

drivers, /dev/watchdog, and the sysfs interface for hardware-specific watchdog code. (3.8)

• The Precision Time Protocol (PTP), defined in IEEE 1588, is enabled. PTP can be used to achieve

synchronization of systems to within a few tens of microseconds. If hardware time-stamping units are

used, synchronization to within a few hundred nanoseconds can be achieved. (3.8)

1.1.4 Cryptography

• An Extended Verification Module (EVM) includes a digital signature that allows file metadata to be

protected by using digital signatures instead of Hashed Message Authentication Control (HMAC). (3.3)

• Kernel modules can now be signed using X.509 certificates. (3.7)

1.1.5 Device Mapper

The device mapper supports an external, read-only device as the origin for a thinly-provisioned volume.

Any reads to the unprovisioned area of the thin device are passed through to this device. For example, a

host could run its guest VMs on thinly provisioned volumes where the base image for all of the VMs resides

on a single device. (3.4)

1.1.6 Diagnostics

• The cpupowerutils feature extends the capabilities of cpufrequtils, and provides statistics for

CPU idle and turbo/boost modes. On AMD systems, it also displays information about boost states and

their frequencies. For more information, see http://lwn.net/Articles/433002/. (3.1)

• zcache version 3 supports multiple clients and in-kernel transcendent memory (tmem) code, and adds

tmem callbacks to support RAMster and corresponding no-op stubs in the zcache driver. New sysfs

parameters provide additional information and allow policy control. (3.1)

1.1.7 DTrace

DTrace is a comprehensive dynamic tracing framework that was initially developed for the Oracle Solaris

operating system. DTrace provides a powerful infrastructure to permit administrators, developers, and

service personnel to concisely answer arbitrary questions about the behavior of the operating system and

user programs in real time.

Note

The DTrace utility packages (dtrace-utils*) are available only on the

Unbreakable Linux Network (ULN).