Jontas » linux

Add a user to a group

jontas — Fri, 03 Dec 2010 10:14:33 +0000

To add a existing user to a group

usermod -a -G thegroup theuser

To add a user to a group when the user is created

useradd -G thegroup theuser

Linux: Finding the serial number of a hard drive

jontas — Fri, 23 Jul 2010 20:33:22 +0000

Finding the serial number of a hard drive on a Linux console (as root) is simple with the right tool.
The right tool in this case is hdparm (using the -i option).
-i will query the device directly for the details.

Example:

themachine:/proc# hdparm -i /dev/sda
 
/dev/sda:
 
 Model=ST31500341AS                            , FwRev=CC1H    , SerialNo=            9VS21ZXM
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=0kB, MaxMultSect=16, MultSect=?16?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=18446744072344861488
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-4,5,6,7
 
 * signifies the current active mode

Using the option -I instead gives even more information:

themachine:/proc# hdparm -I /dev/sda
 
/dev/sda:
 
ATA device, with non-removable media
        Model Number:       ST31500341AS                            
        Serial Number:      9VS21ZXM
        Firmware Revision:  CC1H    
        Transport:          Serial
Standards:
        Used: unknown (minor revision code 0x0029) 
        Supported: 8 7 6 5 
        Likely used: 8
Configuration:
        Logical         max     current
        cylinders       16383   16383
        heads           16      16
        sectors/track   63      63
        --
        CHS current addressable sectors:   16514064
        LBA    user addressable sectors:  268435455
        LBA48  user addressable sectors: 2930277168
        device size with M = 1024*1024:     1430799 MBytes
        device size with M = 1000*1000:     1500301 MBytes (1500 GB)
Capabilities:
        LBA, IORDY(can be disabled)
        Queue depth: 32
        Standby timer values: spec'd by Standard, no device specific minimum
        R/W multiple sector transfer: Max = 16  Current = ?
        Recommended acoustic management value: 254, current value: 0
        DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
             Cycle time: min=120ns recommended=120ns
        PIO: pio0 pio1 pio2 pio3 pio4 
             Cycle time: no flow control=120ns  IORDY flow control=120ns
Commands/features:
        Enabled Supported:
           *    SMART feature set
                Security Mode feature set
           *    Power Management feature set
           *    Write cache
           *    Look-ahead
           *    Host Protected Area feature set
           *    WRITE_BUFFER command
           *    READ_BUFFER command
           *    DOWNLOAD_MICROCODE
                SET_MAX security extension
           *    Automatic Acoustic Management feature set
           *    48-bit Address feature set
           *    Device Configuration Overlay feature set
           *    Mandatory FLUSH_CACHE
           *    FLUSH_CACHE_EXT
           *    SMART error logging
           *    SMART self-test
           *    General Purpose Logging feature set
           *    WRITE_{DMA|MULTIPLE}_FUA_EXT
           *    64-bit World wide name
                Write-Read-Verify feature set
           *    WRITE_UNCORRECTABLE_EXT command
           *    {READ,WRITE}_DMA_EXT_GPL commands
           *    Segmented DOWNLOAD_MICROCODE
           *    SATA-I signaling speed (1.5Gb/s)
           *    SATA-II signaling speed (3.0Gb/s)
           *    Native Command Queueing (NCQ)
           *    Phy event counters
                Device-initiated interface power management
           *    Software settings preservation
           *    SMART Command Transport (SCT) feature set
           *    SCT Long Sector Access (AC1)
           *    SCT LBA Segment Access (AC2)
           *    SCT Error Recovery Control (AC3)
           *    SCT Features Control (AC4)
           *    SCT Data Tables (AC5)
                unknown 206[12] (vendor specific)
Security: 
        Master password revision code = 65534
                supported
        not     enabled
        not     locked
        not     frozen
        not     expired: security count
                supported: enhanced erase
        240min for SECURITY ERASE UNIT. 240min for ENHANCED SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 5000c50014ec1f60
        NAA             : 5
        IEEE OUI        : c50
        Unique ID       : 014ec1f60
Checksum: correct

sudo: unable to resolve host hostname

jontas — Thu, 21 Jan 2010 13:38:15 +0000

If using sudo gives the error message “unable to resolve host hostname” then one solution is to add the hostname in /etc/hosts

127.0.0.1	hostname.domain.com	hostname localhost

Forcing a fsck at next reboot

jontas — Sat, 16 Jan 2010 11:33:36 +0000

Sometimes you wish to make fsck run at the next time (after the computer is powered up/rebooted).
This can be achieved by

Passing F to shutdown

By passing the option “F” to shutdown it will force a file system check at the next boot up.

shutdown -rF now

By creating a /forcefsck file

If the file “/forcefsck” exists then a fsck is forced at boot up.

touch /forcefsck

Turning off auto fsck at boot time

jontas — Sat, 16 Jan 2010 11:23:43 +0000

A Linux machine will auto check the file system if the last shutdown was unclean (the system was powered off before the file system was unmounted) or if it has passed to much time since the last check.

This can be turned off in a few ways, here are some.

[never check] From /etc/fstab

If the sixth option is not 0 (or missing) then fsck will do automatic checking, so change the sixth option to a 0.
As root edit the /etc/fstab (use your favorite text editor or vi).

/dev/sda1		/home/files			ext3	defaults	0 0

[never check] By passing arguments via GRUB

It is possible to pass the option fastboot to the kernel at boot time, this will also prevent fsck from running at boot time.
Edit /boot/grub/menu.lst (use your favorite text editor or vi) [might also be called /etc/grub.conf]
So an example of this would look like

title           Debian GNU/Linux, kernel 2.6.26-1-686
root            (hd0,0)
kernel          /vmlinuz-2.6.26-1-686 root=/dev/mapper/root-root--volume ro fastboot
initrd          /initrd.img-2.6.26-1-686

[only skip once] By passing options to shutdown

If you only wish to bypass the automatic testing of the file system once, but keep the automatic settings saved you can use the shutdown command with the option “f”.
For instance to reboot without checking

shutdown -rf now