Rebooting a Linux Dedicated server with no hard drives from the shell

I just thought I would finally test this so I simulated a complete RAID array failure by pulling all of the drives at once.

This results in an input/output error when trying to do anything so the question is can you still reboot in this situation?

[root@testserver /]# reboot
-bash: /sbin/reboot: Input/output error
[root@testserver /]# shutdown -rn now
-bash: /sbin/shutdown: Input/output error
[root@testserver /]# shutdown
-bash: /sbin/shutdown: Input/output error
[root@testserver /]# uptime
13:47:10 up 41 min,  1 user,  load average: 0.00, 0.00, 0.00

Reboot by sending commands directly to /proc

[root@testserver /]# echo 1 > /proc/sys/kernel/sysrq
[root@testserver /]# echo b > /proc/sysrq-trigger

And sure enough the server rebooted, it could be handy if someone has a remote server without remote hands or remote-reboot (in this case we have both on-site so there was no risk and this was a test server).

What dmesg looks like when the drives are removed and arrays degraded:
[  559.302943] ata3: exception Emask 0x10 SAct 0x0 SErr 0x1810000 action 0xe frozen
[  559.302988] ata3: SError: { PHYRdyChg LinkSeq TrStaTrns }
[  559.303048] ata3: hard resetting link
[  559.303054] ata3: nv: skipping hardreset on occupied port
[  560.024048] ata3: SATA link down (SStatus 0 SControl 300)
[  565.024048] ata3: hard resetting link
[  565.024054] ata3: nv: skipping hardreset on occupied port
[  565.327053] ata3: SATA link down (SStatus 0 SControl 300)
[  565.327064] ata3: limiting SATA link speed to 1.5 Gbps
[  570.327045] ata3: hard resetting link
[  570.327050] ata3: nv: skipping hardreset on occupied port
[  570.630048] ata3: SATA link down (SStatus 0 SControl 300)
[  570.630059] ata3.00: disabled
[  570.630078] ata3: EH complete
[  570.630087] sd 2:0:0:0: rejecting I/O to offline device
[  570.630104] ata3.00: detaching (SCSI 2:0:0:0)
[  570.630125] sd 2:0:0:0: [sda] killing request
[  570.630153] md: super_written gets error=-5, uptodate=0
[  570.630159] md/raid10:md2: Disk failure on sda2, disabling device.
[  570.630162] md/raid10:md2: Operation continuing on 1 devices.
[  570.630257] end_request: I/O error, dev sda, sector 58605128
[  570.630291] md: super_written gets error=-5, uptodate=0
[  570.633517] sd 2:0:0:0: [sda] Synchronizing SCSI cache
[  570.633651] sd 2:0:0:0: [sda]  Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[  570.633659] sd 2:0:0:0: [sda] Stopping disk
[  570.633680] sd 2:0:0:0: [sda] START_STOP FAILED
[  570.633684] sd 2:0:0:0: [sda]  Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[  570.655206] RAID10 conf printout:
[  570.655210]  — wd:1 rd:2
[  570.655214]  disk 0, wo:0, o:1, dev:sdb2
[  570.655217]  disk 1, wo:1, o:0, dev:sda2
[  570.659025] RAID10 conf printout:
[  570.659029]  — wd:1 rd:2
[  570.659032]  disk 0, wo:0, o:1, dev:sdb2
[  570.659313] md: md1 still in use.
[  570.738752] md: md2 still in use.
[  570.739106] md/raid1:md1: Disk failure on sda3, disabling device.
[  570.739109] md/raid1:md1: Operation continuing on 1 devices.
[  570.739380] md/raid10:md0: Disk failure on sda1, disabling device.
[  570.739382] md/raid10:md0: Operation continuing on 1 devices.
[  570.739412] md: unbind<sda2>
[  570.747449] md: export_rdev(sda2)
[  570.868144] RAID1 conf printout:
[  570.868148]  — wd:1 rd:2
[  570.868168]  disk 0, wo:0, o:1, dev:sdb3
[  570.868175]  disk 1, wo:1, o:0, dev:sda3
[  570.873025] RAID1 conf printout:
[  570.873029]  — wd:1 rd:2
[  570.873032]  disk 0, wo:0, o:1, dev:sdb3
[  570.999292] md: unbind<sda3>
[  571.007119] md: export_rdev(sda3)
[  573.633246] ata4: exception Emask 0x10 SAct 0x0 SErr 0x1810000 action 0xe frozen
[  573.633292] ata4: SError: { PHYRdyChg LinkSeq TrStaTrns }
[  573.633331] ata4: hard resetting link
[  573.633335] ata4: nv: skipping hardreset on occupied port
[  574.354052] ata4: SATA link down (SStatus 0 SControl 300)
[  579.354032] ata4: hard resetting link
[  579.354037] ata4: nv: skipping hardreset on occupied port
[  579.657041] ata4: SATA link down (SStatus 0 SControl 300)
[  579.657052] ata4: limiting SATA link speed to 1.5 Gbps
[  584.657032] ata4: hard resetting link
[  584.657038] ata4: nv: skipping hardreset on occupied port
[  584.960047] ata4: SATA link down (SStatus 0 SControl 300)
[  584.960058] ata4.00: disabled
[  584.960076] ata4: EH complete
[  584.960086] sd 3:0:0:0: rejecting I/O to offline device
[  584.960094] ata4.00: detaching (SCSI 3:0:0:0)
[  584.960124] sd 3:0:0:0: [sdb] killing request
[  584.960148] md: super_written gets error=-5, uptodate=0
[  584.960220] end_request: I/O error, dev sdb, sector 58605120
[  584.960265] md: super_written gets error=-5, uptodate=0
[  584.960322] end_request: I/O error, dev sdb, sector 58605128
[  584.960357] md: super_written gets error=-5, uptodate=0
[  584.960393] end_request: I/O error, dev sdb, sector 58605128
[  584.960428] md: super_written gets error=-5, uptodate=0
[  584.962495] sd 3:0:0:0: [sdb] Synchronizing SCSI cache
[  584.962765] sd 3:0:0:0: [sdb]  Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[  584.962772] sd 3:0:0:0: [sdb] Stopping disk
[  584.962786] Buffer I/O error on device md2, logical block 524292
[  584.962805] sd 3:0:0:0: [sdb] START_STOP FAILED
[  584.962810] sd 3:0:0:0: [sdb]  Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[  584.962824] lost page write due to I/O error on md2
[  584.962841] end_request: I/O error, dev sdb, sector 58605128
[  584.962877] md: super_written gets error=-5, uptodate=0
[  584.962921] md: md1 still in use.
[  584.962931] Buffer I/O error on device md2, logical block 524293
[  584.963007] lost page write due to I/O error on md2
[  584.963020] Buffer I/O error on device md2, logical block 1048646
[  584.963095] lost page write due to I/O error on md2
[  584.963104] Buffer I/O error on device md2, logical block 1048647
[  584.963179] lost page write due to I/O error on md2
[  584.963188] Buffer I/O error on device md2, logical block 1048648
[  584.963274] lost page write due to I/O error on md2
[  584.963280] md: md2 still in use.
[  584.963299] Buffer I/O error on device md2, logical block 1048694
[  584.963381] lost page write due to I/O error on md2
[  584.963391] Buffer I/O error on device md2, logical block 1056863
[  584.963468] lost page write due to I/O error on md2
[  584.963478] Buffer I/O error on device md2, logical block 1056864
[  584.963553] lost page write due to I/O error on md2
[  584.963562] Buffer I/O error on device md2, logical block 6299690
[  584.963635] lost page write due to I/O error on md2
[  584.963800] Aborting journal on device md2-8.
[  584.963836] EXT4-fs error (device md2) in ext4_delete_inode: Readonly filesystem
[  584.963868] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 987 pages, ino 28972747; err -30
[  584.963877] md: super_written gets error=-19, uptodate=0
[  584.963883]
[  584.963888] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 7896 pages, ino 28972690; err -30
[  584.963893]
[  584.963953] EXT4-fs warning (device md2): ext4_end_bio: I/O error writing to inode 28972747 (size 36864 starting block 689771)
[  584.964303] JBD2: I/O error detected when updating journal superblock for md2-8.
[  584.964309] EXT4-fs error (device md2): ext4_journal_start_sb: Detected aborted journal
[  584.964316] EXT4-fs (md2): Remounting filesystem read-only
[  584.972785] md0: detected capacity change from 30005002240 to 0
[  584.972794] md: md0 stopped.
[  584.972810] md: unbind<sdb1>
[  584.979298] md: export_rdev(sdb1)
[  584.979344] md: unbind<sda1>
[  584.987280] md: export_rdev(sda1)
[  585.165084] md: super_written gets error=-19, uptodate=0
[  585.165102] md: super_written gets error=-19, uptodate=0
[  589.309845] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  589.963162] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 263495; err -30
[  589.963314]
[  599.310238] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  604.963046] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 262464; err -30
[  604.963153]
[  609.310592] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  614.963071] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 28186168; err -30
[  614.963176]
[  614.963181] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 8192 pages, ino 28186171; err -30
[  614.963298]
[  614.963301] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 8192 pages, ino 28972747; err -30
[  614.963405]
[  614.963408] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 8192 pages, ino 28972690; err -30
[  614.963507]
[  619.310906] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  619.963133] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 263495; err -30
[  619.963244]
[  629.311267] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  634.963038] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 262464; err -30
[  634.963144]
[  639.311561] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  644.963069] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 28186168; err -30
[  644.963172]
[  644.963176] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 8192 pages, ino 28186171; err -30
[  644.963288]
[  644.963291] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 8192 pages, ino 28972747; err -30
[  644.963395]
[  644.963397] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 8192 pages, ino 28972690; err -30
[  644.963499]
[  649.311846] EXT4-fs error (device md2): ext4_find_entry: reading directory #262476 offset 0
[  649.963202] EXT4-fs (md2): ext4_da_writepages: jbd2_start: 1024 pages, ino 263495; err -30
[  649.963319]
[  653.202216] ata3: exception Emask 0x10 SAct 0x0 SErr 0x50000 action 0xe frozen
[  653.202317] ata3: SError: { PHYRdyChg CommWake }
[  653.202379] ata3: hard resetting link