GNUのcpコマンドには、sparseオプションがありこれを使うと、
ファイルとしてはそのままに、実際にディスクを使用する量を削減することができる可能性があります。

使い方は、以下のような感じです。

$ dd if=/dev/zero of=hoge.img bs=1024 count=102400
$ cp --sparse=always hoge.img hoge.img.sparse
$ ls -lhs
合計 101M
101M -rw-r--r-- 1 igawa igawa 100M 2010-06-08 22:16 hoge.img
   0 -rw-r--r-- 1 igawa igawa 100M 2010-06-08 22:17 hoge.img.sparse
^^^^実際にディスクを使用しているサイズ。(今回の場合、ゼロバイト！)

実際にディスクを使用しているサイズは、上記のようにlsコマンドの「s」オプションで確認できます。

さらに、sparse fileのまま、tarボールにすることもできます。

$ tar -Szcvf hoge.img.sparse.tar.gz hoge.img.sparse
$ ls -lhs hoge.img.sparse.tar.gz
4.0K -rw-r--r-- 1 igawa igawa 139 2010-06-08 22:32 hoge.img.sparse.tar.gz

普通にtarボールにした場合

$ tar -zcvf hoge.img.sparse.tar.gz hoge.img.sparse
hoge.img.sparse
$ ls -lhs hoge.img.sparse.tar.gz
104K -rw-r--r-- 1 igawa igawa 100K 2010-06-08 22:35 hoge.img.sparse.tar.gz

sparse fileについては、こちらが参考になると思います。

http://en.wikipedia.org/wiki/Sparse_file

要は、何もデータが無い領域は、削除して「あるかのように見せる」ということをしている様です。
なので、通常のファイルの場合は削減効果はあまり期待できません。

削減を期待できるのは、仮想OSの仮想ディスクファイルや、メモリダンプイメージなどでしょう。

Linux kernelのmakeのターゲットでありそうな気もするんですが、見つからなかったので。

$ cat make_oldconfig_auto.sh

#!/usr/bin/env expect

set timeout 10
spawn make oldconfig
while {1} {
        expect {
                "] (NEW)" { send "\n" }
                "# configuration written to .config" {break}
        }
}

interact

見てわかるとおり、expectを使って、”] (NEW)”というのが出てきたら、Enter入力。
“# configuration written to .config”が出てきたらおしまい。

というスクリプトです。

Linux kernel makeの結果はTwitterにつぶやくことにした。

ほとんどのBlog記事が、そればかりになりそうなのでw

kernel make stderr outputs:

crypto/anubis.c: In function ‘anubis_crypt’:
crypto/anubis.c:581: 警告: ‘inter’ is used uninitialized in this function
drivers/acpi/acpi_pad.c: In function ‘acpi_pad_handle_notify’:
drivers/acpi/acpi_pad.c:420: 警告: ‘num_cpus’ may be used uninitialized in this function
fs/minix/dir.c: In function ‘dir_get_page’:
fs/minix/dir.c:79: 警告: label ‘fail’ defined but not used
drivers/isdn/hardware/mISDN/hfcpci.c: In function ‘hfcpci_softirq’:
drivers/isdn/hardware/mISDN/hfcpci.c:2320: 警告: ignoring return value of ‘driver_for_each_device’, declared with attribute warn_unused_result
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c: In function ‘i2o_cfg_passthru’:
drivers/message/i2o/i2o_config.c:878: 警告: 異なるサイズの整数からポインタにキャストされました
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c:933: 警告: 異なるサイズの整数からポインタにキャストされました
drivers/misc/enclosure.c: In function ‘enclosure_component_register’:
drivers/misc/enclosure.c:289: 警告: ignoring return value of ‘ERR_PTR’, declared with attribute warn_unused_result
drivers/pci/pcie/aer/aerdrv_core.c: In function ‘aer_isr’:
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.id’ may be used uninitialized in this function
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.status’ may be used uninitialized in this function
drivers/xen/events.c:135: 警告: ‘mk_pirq_info’ defined but not used
drivers/xen/events.c:181: 警告: ‘gsi_from_irq’ defined but not used
drivers/xen/events.c:191: 警告: ‘vector_from_irq’ defined but not used
drivers/video/via/via-gpio.c: In function ‘viafb_gpio_probe’:
drivers/video/via/via-gpio.c:216: 警告: assignment from incompatible pointer type
WARNING: modpost: Found 43 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
/home/igawa/src/linux-2.6/usr/include/drm/drm_mode.h:84: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/i915_drm.h:119: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/mga_drm.h:260: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/radeon_drm.h:758: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/via_drm.h:117: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/linux/virtio_9p.h:15: found __[us]{8,16,32,64} type without #include

Root device is (8, 1)
Setup is 13580 bytes (padded to 13824 bytes).
System is 3577 kB
CRC 55ea96c
WARNING: modpost: Found 5 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

real	14m8.840s
user	44m36.700s
sys	6m39.545s
ERROR: modinfo: could not find module k10temp

kernel make stderr outputs:

crypto/anubis.c: In function ‘anubis_crypt’:
crypto/anubis.c:581: 警告: ‘inter’ is used uninitialized in this function
drivers/acpi/acpi_pad.c: In function ‘acpi_pad_handle_notify’:
drivers/acpi/acpi_pad.c:420: 警告: ‘num_cpus’ may be used uninitialized in this function
fs/minix/dir.c: In function ‘dir_get_page’:
fs/minix/dir.c:79: 警告: label ‘fail’ defined but not used
drivers/isdn/hardware/mISDN/hfcpci.c: In function ‘hfcpci_softirq’:
drivers/isdn/hardware/mISDN/hfcpci.c:2320: 警告: ignoring return value of ‘driver_for_each_device’, declared with attribute warn_unused_result
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c: In function ‘i2o_cfg_passthru’:
drivers/message/i2o/i2o_config.c:878: 警告: 異なるサイズの整数からポインタにキャストされました
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c:933: 警告: 異なるサイズの整数からポインタにキャストされました
drivers/misc/enclosure.c: In function ‘enclosure_component_register’:
drivers/misc/enclosure.c:289: 警告: ignoring return value of ‘ERR_PTR’, declared with attribute warn_unused_result
drivers/pci/pcie/aer/aerdrv_core.c: In function ‘aer_isr’:
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.id’ may be used uninitialized in this function
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.status’ may be used uninitialized in this function
drivers/xen/events.c:135: 警告: ‘mk_pirq_info’ defined but not used
drivers/xen/events.c:181: 警告: ‘gsi_from_irq’ defined but not used
drivers/xen/events.c:191: 警告: ‘vector_from_irq’ defined but not used
drivers/video/via/via-gpio.c: In function ‘viafb_gpio_probe’:
drivers/video/via/via-gpio.c:216: 警告: assignment from incompatible pointer type
WARNING: modpost: Found 43 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
/home/igawa/src/linux-2.6/usr/include/drm/drm_mode.h:84: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/i915_drm.h:119: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/mga_drm.h:260: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/radeon_drm.h:758: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/via_drm.h:117: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/linux/virtio_9p.h:15: found __[us]{8,16,32,64} type without #include

Root device is (8, 1)
Setup is 13580 bytes (padded to 13824 bytes).
System is 3577 kB
CRC 9ed9bd2b
WARNING: modpost: Found 5 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

real	14m10.199s
user	44m34.740s
sys	6m39.784s
ERROR: modinfo: could not find module k10temp

kernel make stderr outputs:

crypto/anubis.c: In function ‘anubis_crypt’:
crypto/anubis.c:581: 警告: ‘inter’ is used uninitialized in this function
drivers/acpi/acpi_pad.c: In function ‘acpi_pad_handle_notify’:
drivers/acpi/acpi_pad.c:420: 警告: ‘num_cpus’ may be used uninitialized in this function
fs/minix/dir.c: In function ‘dir_get_page’:
fs/minix/dir.c:79: 警告: label ‘fail’ defined but not used
drivers/isdn/hardware/mISDN/hfcpci.c: In function ‘hfcpci_softirq’:
drivers/isdn/hardware/mISDN/hfcpci.c:2320: 警告: ignoring return value of ‘driver_for_each_device’, declared with attribute warn_unused_result
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c: In function ‘i2o_cfg_passthru’:
drivers/message/i2o/i2o_config.c:878: 警告: 異なるサイズの整数からポインタにキャストされました
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c:933: 警告: 異なるサイズの整数からポインタにキャストされました
drivers/misc/enclosure.c: In function ‘enclosure_component_register’:
drivers/misc/enclosure.c:289: 警告: ignoring return value of ‘ERR_PTR’, declared with attribute warn_unused_result
drivers/pci/pcie/aer/aerdrv_core.c: In function ‘aer_isr’:
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.id’ may be used uninitialized in this function
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.status’ may be used uninitialized in this function
drivers/xen/events.c:135: 警告: ‘mk_pirq_info’ defined but not used
drivers/xen/events.c:181: 警告: ‘gsi_from_irq’ defined but not used
drivers/xen/events.c:191: 警告: ‘vector_from_irq’ defined but not used
drivers/video/via/via-gpio.c: In function ‘viafb_gpio_probe’:
drivers/video/via/via-gpio.c:216: 警告: assignment from incompatible pointer type
WARNING: modpost: Found 43 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
/home/igawa/src/linux-2.6/usr/include/drm/drm_mode.h:84: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/i915_drm.h:119: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/mga_drm.h:260: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/radeon_drm.h:758: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/via_drm.h:117: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/linux/virtio_9p.h:15: found __[us]{8,16,32,64} type without #include

Root device is (8, 1)
Setup is 13580 bytes (padded to 13824 bytes).
System is 3577 kB
CRC fd82830b
WARNING: modpost: Found 5 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

real	14m8.479s
user	44m35.258s
sys	6m40.742s
ERROR: modinfo: could not find module k10temp

kernel make stderr outputs:

crypto/anubis.c: In function ‘anubis_crypt’:
crypto/anubis.c:581: 警告: ‘inter’ is used uninitialized in this function
drivers/acpi/acpi_pad.c: In function ‘acpi_pad_handle_notify’:
drivers/acpi/acpi_pad.c:420: 警告: ‘num_cpus’ may be used uninitialized in this function
fs/minix/dir.c: In function ‘dir_get_page’:
fs/minix/dir.c:79: 警告: label ‘fail’ defined but not used
drivers/isdn/hardware/mISDN/hfcpci.c: In function ‘hfcpci_softirq’:
drivers/isdn/hardware/mISDN/hfcpci.c:2320: 警告: ignoring return value of ‘driver_for_each_device’, declared with attribute warn_unused_result
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c: In function ‘i2o_cfg_passthru’:
drivers/message/i2o/i2o_config.c:878: 警告: 異なるサイズの整数からポインタにキャストされました
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c:933: 警告: 異なるサイズの整数からポインタにキャストされました
drivers/misc/enclosure.c: In function ‘enclosure_component_register’:
drivers/misc/enclosure.c:289: 警告: ignoring return value of ‘ERR_PTR’, declared with attribute warn_unused_result
drivers/pci/pcie/aer/aerdrv_core.c: In function ‘aer_isr’:
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.id’ may be used uninitialized in this function
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.status’ may be used uninitialized in this function
drivers/xen/events.c:135: 警告: ‘mk_pirq_info’ defined but not used
drivers/xen/events.c:181: 警告: ‘gsi_from_irq’ defined but not used
drivers/xen/events.c:191: 警告: ‘vector_from_irq’ defined but not used
drivers/video/via/via-gpio.c: In function ‘viafb_gpio_probe’:
drivers/video/via/via-gpio.c:216: 警告: assignment from incompatible pointer type
WARNING: modpost: Found 43 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
/home/igawa/src/linux-2.6/usr/include/drm/drm_mode.h:84: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/i915_drm.h:119: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/mga_drm.h:260: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/radeon_drm.h:758: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/via_drm.h:117: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/linux/virtio_9p.h:15: found __[us]{8,16,32,64} type without #include

Root device is (8, 1)
Setup is 13564 bytes (padded to 13824 bytes).
System is 3577 kB
CRC f91db09a
WARNING: modpost: Found 1 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

real	14m9.572s
user	44m38.599s
sys	6m39.779s
ERROR: modinfo: could not find module k10temp

kernel make stderr outputs:

crypto/anubis.c: In function ‘anubis_crypt’:
crypto/anubis.c:581: 警告: ‘inter’ is used uninitialized in this function
drivers/acpi/acpi_pad.c: In function ‘acpi_pad_handle_notify’:
drivers/acpi/acpi_pad.c:420: 警告: ‘num_cpus’ may be used uninitialized in this function
drivers/isdn/hardware/mISDN/hfcpci.c: In function ‘hfcpci_softirq’:
drivers/isdn/hardware/mISDN/hfcpci.c:2320: 警告: ignoring return value of ‘driver_for_each_device’, declared with attribute warn_unused_result
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c: In function ‘i2o_cfg_passthru’:
drivers/message/i2o/i2o_config.c:878: 警告: 異なるサイズの整数からポインタにキャストされました
In file included from drivers/message/i2o/config-osm.c:40:
drivers/message/i2o/i2o_config.c:933: 警告: 異なるサイズの整数からポインタにキャストされました
drivers/misc/enclosure.c: In function ‘enclosure_component_register’:
drivers/misc/enclosure.c:289: 警告: ignoring return value of ‘ERR_PTR’, declared with attribute warn_unused_result
drivers/pci/pcie/aer/aerdrv_core.c: In function ‘aer_isr’:
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.id’ may be used uninitialized in this function
drivers/pci/pcie/aer/aerdrv_core.c:756: 警告: ‘e_src.status’ may be used uninitialized in this function
drivers/xen/events.c:135: 警告: ‘mk_pirq_info’ defined but not used
drivers/xen/events.c:181: 警告: ‘gsi_from_irq’ defined but not used
drivers/xen/events.c:191: 警告: ‘vector_from_irq’ defined but not used
drivers/video/via/via-gpio.c: In function ‘viafb_gpio_probe’:
drivers/video/via/via-gpio.c:216: 警告: assignment from incompatible pointer type
WARNING: modpost: Found 43 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
/home/igawa/src/linux-2.6/usr/include/drm/drm_mode.h:84: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/i915_drm.h:119: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/mga_drm.h:260: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/radeon_drm.h:758: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/drm/via_drm.h:117: found __[us]{8,16,32,64} type without #include

/home/igawa/src/linux-2.6/usr/include/linux/virtio_9p.h:15: found __[us]{8,16,32,64} type without #include

Root device is (8, 1)
Setup is 13580 bytes (padded to 13824 bytes).
System is 3575 kB
CRC dea2ebd4
WARNING: modpost: Found 2 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'

real	14m35.363s
user	45m5.107s
sys	7m2.156s
ERROR: modinfo: could not find module k10temp

kernel make stderr outputs:

make[1]: *** [silentoldconfig] Error 1
make: *** [silentoldconfig] Error 2

kernel make stderr outputs:

make[1]: *** [silentoldconfig] Error 1
make: *** [silentoldconfig] Error 2