Operating Systems

New Features for Linux on System z

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This article examines three newly developed features for Linux on System z:

  • Tools for changing re-IPL and shutdown settings
  • Tools to dynamically change the memory footprint of a Linux instance
  • The cmsfs File System in Userspace (FUSE) for accessing z/VM CMS formatted DASD.

These programs are part of the s390-tools open source package included in all major Linux distributions; they can be downloaded at www.ibm.com/developerworks/linux/linux390/s390-tools.html.

The Re-IPL and Shutdown Action Tools

s390-tools version 1.8.0 includes four new utilities—lsreipl, chreipl, lsshut, and chshut—to control and show Linux re-IPL settings and actions taken after shutdown. They use a sysfs interface accessible via the /sys/firmware directory.

Re-IPL tools: These tools can show from which device the current system was booted (IPL setting) and show or change the device to be used for the next reboot (re-IPL setting). Changing the reboot device from your Linux shell can be beneficial. You can switch between multiple installed operating systems (e.g., different Linux distributions) or kernel levels without requiring the HMC or a 3270 terminal. Consider software development tests that must be done on different Linux levels. A script could automate that process by booting the next operating system after the tests are completed. Another example is a Linux installer program that can automatically boot from the newly prepared disk after installation.

The lsreipl tool shows current re-IPL or IPL settings and chreipl changes the re-IPL settings.

With the chreipl tool, you can use the ccw of fcp keyword to specify use of a DASD or SCSI disk for the next reboot. With the node keyword, you can also specify the disk through its standard device node (e.g., /dev/dasdxy or /dev/sdxy). The syntax of the tool is:

  • DASD: chreipl ccw <bus-ID> [-L <LOADPARM>]
  • SCSI: chreipl fcp <bus-ID> <WWPN> <LUN> [-b <BOOTPROG>]
  • DASD and SCSI: chreipl node <DEVICE NODE> [-L <LOADPARM>] [-b <BOOTPROG>].

By using loadparm for DASD and bootprog for SCSI devices, you can select a zipl boot menu. Figure 1 shows several actual use examples.

 

The tools use the sysfs kernel interface under the /sys/firmware directory. The Linux sysfs is a virtual file system, similar to the well-known procfs file system, and is used for kernel to user space communication. For example, when changing the re-IPL device to DASD 4e10, the chreipl tool writes 0.0.4e10 to the /sys/firmware/reipl/ccw/device file and ccw to the /sys/firmware/reipl/reipl_type file. The lsreipl tool reads and prints the contents of the respective files.

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