How can I tell what I/O scheduler I'm using on RH4?

[Barry Brimer]

Quoting Yong Huang <yong321 at yahoo.com>:

> On RH5, I can tell what I/O scheduler I'm using:
>
> $ uname -a
> Linux thehostname 2.6.18-92.1.13.el5 #1 SMP Thu Sep 4 03:51:21 EDT 2008
> x86_64 x86_64 x86_64 GNU/Linux
> $ cat /etc/redhat-release
> Red Hat Enterprise Linux Server release 5.2 (Tikanga)
> $ cd /sys/block/sda/queue
> $ ls -l
> total 0
> drwxr-xr-x 2 root root    0 Nov 26 13:43 iosched
> -r--r--r-- 1 root root 4096 Jan 12 23:12 max_hw_sectors_kb
> -rw-r--r-- 1 root root 4096 Jan 12 23:12 max_sectors_kb
> -rw-r--r-- 1 root root 4096 Jan 12 23:12 nr_requests
> -rw-r--r-- 1 root root 4096 Jan 12 23:12 read_ahead_kb
> -rw-r--r-- 1 root root 4096 Jan 12 23:12 scheduler
> $ cat scheduler
> noop anticipatory deadline [cfq]
>
> So I'm using CFQ. But on RH4, there's no /sys/block/sda/queue/scheduler:
>
> $ uname -a
> Linux hostname 2.6.9-55.ELsmp #1 SMP Fri Apr 20 16:36:54 EDT 2007 x86_64
> x86_64 x86_64 GNU/Linux
> $ cat /etc/redhat-release
> Red Hat Enterprise Linux AS release 4 (Nahant Update 7)
> $ ls -l /sys/block/sda/queue
> total 0
> drwxr-xr-x  2 root root    0 Jan 13 11:03 iosched
> -r--r--r--  1 root root 4096 Jan 13 11:02 max_hw_sectors_kb
> -rw-r--r--  1 root root 4096 Jan 13 11:02 max_sectors_kb
> -rw-r--r--  1 root root 4096 Jan 13 11:02 nr_requests
> -rw-r--r--  1 root root 4096 Jan 13 11:02 read_ahead_kb
>
> I checked grub.conf. Neither box has an entry for I/O scheduler.

cfq is the default scheduler on RHEL 4.

grep scheduler /var/log/messages* (provided that there are still logs from when
the system booted)