Rolling shells

Something interesting i spotted on Karansbir’s blog:

Running dstat normally gives you something like this :

# dstat --nocolor
----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read  writ| recv  send|  in   out | int   csw
  3   0  97   0   0   0| 820k  456k|   0     0 | 800B  866B|1054   255

And you can split the disk metrics up based on devices using something like this :

# dstat -D sda,sdb,total --nocolor
----total-cpu-usage---- --dsk/sda-- --dsk/sdb-- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read  writ: read  writ: read  writ| recv  send|  in   out | int   csw
  1   1  97   0   0   0| 176k   77k:  30k  162k: 411k  478k|   0     0 |3608B 4005B|1447  1458
 33   2  63   0   1   2|   0     0 :   0   216k:   0   432k|2470k 1611k|   0     0 |2915  6967
 31   2  65   0   1   1|   0     0 :   0     0 :   0     0 |2210k 1338k|   0     0 |2866  6051

But you can also get deeper level device names / nodes to measure – which is required in many cases if you have drivers for storage creating nodes further down the tree than /dev. Eg. I have a setup where there are four mysql instances running, each with its own dedicated storage :

# mount | grep srv
/dev/cciss/c0d1 on /var/lib/mysql/node1 type ext3 (rw)
/dev/cciss/c0d2 on /var/lib/mysql/node2 type ext3 (rw)
/dev/cciss/c0d3 on /var/lib/mysql/node3 type ext3 (rw)
/dev/cciss/c0d4 on /var/lib/mysql/node4 type ext3 (rw)
/dev/cciss/c0d5 on /srv/wal type ext3 (rw)

so in this case, to get dstat reporting working you need to mention just the component level, like this :

# dstat -D cciss/c0d1,cciss/c0d2,cciss/c0d3 --nocolor
----total-cpu-usage---- dsk/cciss/c dsk/cciss/c dsk/cciss/c -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read  writ: read  writ: read  writ| recv  send|  in   out | int   csw
  3   0  97   0   0   0| 209k   89k: 201k   86k: 204k   85k|   0     0 | 799B  865B|1055   256
 90   1   8   1   0   0|3196k   68k: 764k    0 : 816k   24k|1067k 1650k|   0     0 |1999   609
 95   1   3   1   0   0|2548k    0 :   0  4084k:2448k 5700k| 660k  791k|   0     0 |1611   571
 96   1   2   1   0   0|2628k    0 : 808k    0 :1620k    0 | 352k  798k|   0     0 |1835  1605

And you get the details, for each block device.

yesterday i run true a weird situation. After installing fresh DomU with xen-image-create via debootstrap, I noticed that its ipbtales is not working giving the following:

WARNING: Could not open 'kernel/net/netfilter/x_tables.ko': No such file or directory
FATAL: Could not open 'kernel/net/ipv4/netfilter/ip_tables.ko': No such file or directory
iptables v1.3.6: can't initialize iptables table `filter': iptables who? (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.

anyway its very easy to fix and i just decided to share the info, just type a simple command:

depmod

If you have problems with xen domU console on Debian 5.0 Lenny, stoping at crond, try to add the following line to your config:

extra = 'console=hvc0 xencons=tty'