Moving /tmp to RAM? Moving system from USB keydrive to SD card?

littlebigman · 04-03-2015, 08:57 AM

Hello

I have a couple of questions about running Debian on an ARM appliance:

1. To avoid wearing out flash memory, I'd like to move /tmp from the flash memory to RAM: Is it a good idea, and if yes, how should I proceed?*

2. The system is currently booting and running off a USB keydrive and I'd like to move it an SD card wihtout going through the whole setup again: Can I copy it from the USB keydrive to the SD card? How should I do this?

Thank you.

* Here's the infos about the device:

Code:

# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
udev on /dev type devtmpfs (rw,relatime,size=10240k,nr_inodes=63461,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,noexec,relatime,size=51512k,mode=755)
/dev/disk/by-uuid/a82663a4-cc9d-4551-b1a3-704eccf43343 on / type ext4 (rw,relatime,errors=remoun            t-ro,user_xattr,barrier=1,data=ordered)
tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
tmpfs on /run/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=147240k)
/dev/sda1 on /boot type ext2 (rw,relatime,errors=continue)

# blkid
/dev/sda5: UUID="a30ad772-7f50-43ee-ad2b-32aedbb1abce" TYPE="swap"
/dev/sda1: UUID="fa73e058-e340-4ebc-ad94-30fddfd9fdfd" TYPE="ext2"
/dev/sda2: UUID="a82663a4-cc9d-4551-b1a3-704eccf43343" TYPE="ext4"
/dev/mmcblk0p1: LABEL="SHEEVAPLUG" UUID="FE1A-7167" TYPE="vfat"

# fdisk -l

; This is the USB keydrive
Disk /dev/sda: 3999 MB, 3999268864 bytes
124 heads, 62 sectors/track, 1016 cylinders, total 7811072 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000bbc04

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      444415      221184   83  Linux
/dev/sda2          444416     7364607     3460096   83  Linux
/dev/sda3         7366654     7809023      221185    5  Extended
/dev/sda5         7366656     7809023      221184   82  Linux swap / Solaris

; This is the empty SD card
Disk /dev/mmcblk0: 16.0 GB, 16012804096 bytes
255 heads, 63 sectors/track, 1946 cylinders, total 31275008 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x40c68308

        Device Boot      Start         End      Blocks   Id  System
/dev/mmcblk0p1            2048    31275007    15636480    c  W95 FAT32 (LBA)

# lshw -short
H/W path        Device     Class      Description
=================================================
/0/0                       memory     503MiB System memory
/0/2            scsi0      storage
/0/2/0.0.0      /dev/sda   disk       3999MB SCSI Disk
/0/2/0.0.0/1    /dev/sda1  volume     216MiB Linux filesystem partition
/0/2/0.0.0/2    /dev/sda2  volume     3379MiB EXT4 volume
/0/2/0.0.0/3    /dev/sda3  volume     216MiB Extended partition
/0/2/0.0.0/3/5  /dev/sda5  volume     216MiB Linux swap / Solaris partition

schneidz · 04-03-2015, 09:05 AM

is the sd-card bigger than the usb drive ?
dd mite work. dd is very destructive if you cross drives. something like:

Code:

dd if=/dev/sdx of=/dev/sdy bs=8192

TobiSGD · 04-03-2015, 10:04 AM

Quote:

Originally Posted by littlebigman

1. To avoid wearing out flash memory, I'd like to move /tmp from the flash memory to RAM: Is it a good idea, and if yes, how should I proceed?*

Yes, that is a good idea and basically comes down to adding this line to your /etc/fstab:

Code:

tmpfs                   /tmp                    tmpfs   mode=1777       0 0

By default space in tmp, when using tmpfs, is limited to half your RAM, you can adjust that using the size= mount option.
If you are using Debian Testing/Jessie with systemd you don't need to do that, /tmp is automatically mounted as a tmpfs in that case.

Quote:

2. The system is currently booting and running off a USB keydrive and I'd like to move it an SD card wihtout going through the whole setup again: Can I copy it from the USB keydrive to the SD card? How should I do this?

As schneidz already said, if your SD card is as large as the USB device or larger, just use dd to copy the system over.