backups" -- Technical Information" "

Strategies for backing up COHERENT
This entry describes how to backup files -- that is, how to copy one or more selected files onto floppy disks. You should do this regularly to provide yourself with a spare copy of valuable files should your system suffer a catastrophe.

The strategy you adopt for backups will vary quite a bit, depending upon the medium onto which you back up your files: tapes or floppy disks. Floppy disks are inexpensive, but their limited capacity means that you have to plan carefully. Tapes are simpler to use than floppy disks, but are more expensive. The following sections describe first the strategies for backing up onto floppy disks; and then for backing up onto tapes.

Backing up Onto Floppy Disks

There are two general strategies for backing up files onto floppy disks:

+o
Use the command tar to create archives of files on a floppy disk. This is fine for archiving a limited set of files on an irregular basis.

+o
The other strategy uses the command gnucpio to implement a system of regular dumps. This strategy is preferred for systems that daily amass data of importance for a real-world job, such as running a business or managing a research project.

You should always have a procedure of backups for your system. Which strategy you use depends on how you are using your system. The following sections describe how to implement each strategy of backups. Note that COHERENT includes a version of the UNIX utility dump for the sake of compatibility with older versions of UNIX and COHERENT; however, dump is obsolete, should not be used, and will not be described here.

Please note that the following descriptions assume that you are using a 5.25-inch, high-density floppy disks set in drive 0 (drive A). For a list of available floppy-disk devices, see the Lexicon entry for floppy disks.

The following describes how to use tar to back up onto floppy disks.

The first step is to prepare floppy disks to receive files. Insert a 5.25-inch floppy disk into drive 0, and then type the following command: 

     /etc/fdformat -v /dev/rfha0

The command fdformat formats the floppy disk, verifying that no media defects exist. You must perform this task of formatting a floppy disk before you use it the first time.

The next step is to create an archive of the files you wish to back up. Use the portable archive command tar to collect a mass of files into an archive on the floppy disks. For example, to archive all files in directory ssoouurrccee, use the following command: 

     tar cvf /dev/rfha0 source

The options ccvvff tell ttaarr to create an archive, run in verbose mode, and write the archive onto the device or into the file named in the next argument. //ddeevv//rrffhhaa00 names the floppy device onto which you wish to write the archive. Finally, ssoouurrccee is the directory whose files you wish to back up.

To perform a listing of the contents of the newly created archive, type 

     tar tvf /dev/rfha0

The options ttvvff tell ttaarr to list the contents of the archive, run in verbose mode, and read the archive from the device or file named in the next argument.

To extract several files from the archive, enter a command of the form 

     tar xvf /dev/rfha0 source/myfile 'source/*.c'

The options xxvvff tell ttaarr to extract or unarchive the specified files, run in verbose mode, and read the archive from the device or file named in the next argument. Note that the second file argument contains a ``wildcard'' character and thus must be quoted to prevent expansion by the shell.

For more information on how to use tar, see its entry in the Lexicon.

The following describes how to back up using gnucpio.

The COHERENT utility gnucpio performs mass dumps and restores of files using a universally recognized file format.

In this example, dumps are performed monthly, weekly, and daily. You should prepare at least three sets of floppy disks for the monthly saves, giving you three months of full backup. You will use the floppy disks in rotation, with the oldest always used next.

Once a month, you should dump the entire system.

Once a week, you should dump information in the system that is new or has been changed since the end of the previous week. You will need five sets of floppy disks, because some months have five weekends in them.

Finally, every day you should save information that has changed that day. For these dumps, you will need five sets of floppy disks: one for each working day. You may need extras in case of weekend work.

Label each set of disks carefully as _m_o_n_t_h_l_y, _w_e_e_k_l_y, or _d_a_i_l_y. Label the daily floppy disks ``Monday'' through ``Friday'', the weekly floppy disks ``Week 1'' through ``Week 5'', and the monthly floppy disks ``Month 1'' through ``Month 3''. When you perform the dump, write the date on the label.

The following gives a step-by-step description of how to use gnucpio to back up files. The next samples are given with the suggestion that your system has only one 5.25-inch floppy-disk drive.

1.
Log into the system as the superuser root.

2.
If you have not yet done so, use the command fdformat to format a set of floppy disks, as shown above. With high-density, 5.25-inch floppy disks, a rule of thumb is to prepare one floppy disk for each megabyte of data to be dumped.

3.
If other users are logged into the system, use the command wall to request that they log off. For example: 
     /etc/wall
     Please log off.
     Time for file dump.
     <ctrl-D>

4.
Be sure that all users are logged off the system by typing the command: 
     who

This command names all users who are still on the system.

If they have not logged off in a few minutes, send another message. Repeat the process until who shows no users except yourself.

5.
When all other users have logged off, execute the command shutdown as described in its Lexicon entry.

6.
Run the script mount.all to mount all of your file systems. Then, run the COHERENT command fsck on each file system to check its integrity.

7.
If this is the last workday of the month, perform a _m_o_n_t_h_l_y dump, to back up the entire system. Insert the first volume of the correct monthly dump floppy disk into the floppy drive, after adding today's date to the label, and type the commands: 
     cd /
     find . -print | gnucpio -ocF /dev/rfha0

Option -F tells gnucpio to write everything to the raw, 2400-block, floppy-disk device /dev/rfha0.

Note that if you want to split your dump across different media (i.e., write the first volume onto tape and the second onto a floppy disk), you should not use the option -F; gnucpio will write its output to the standard output, and you can use the shell operator `>' to redirect that to the device /dev/rfha0. If you do not use -F, gnucpio will ask you, after it finishes writing a volume, for the name of the device into which it should redirect the next volume of output.

As more floppies are needed, gnucpio will ask you to insert them. Be sure to label each floppy disk with its volume number.

8.
If this is the last work day of the week, but not the last workday of the month, perform a _w_e_e_k_l_y dump. Prepare the correct weekly dump floppy disks, add today's date to the label, insert the first floppy disk, and type the command: 
     cd /
     find . -newer cpio.weekly -print | gnucpio -ocF /dev/rfha0
     touch cpio.weekly

This will dump all files that are younger than file cpios.weekly.

9.
If this is neither the last workday of the month nor the last workday of the week, you will perform a _d_a_i_l_y dump. Prepare the daily dump floppy disk with today's day of the week, add today's date to the label, insert the first floppy disk into the drive, and type the command: 
     cd /
     find . -newer cpio.daily -print | gnucpio -ocF /dev/rfha0
     touch cpio.daily

This will dump files that are younger than file cpio.daily.

10.
Type sync to ensure that all buffers are flushed.

11.
When you are finished dumping data, type the command /etc/reboot to return your system to multi- user mode.

For more information on how to use gnucpio and find, see their respective entries in the Lexicon.

If you wish, you can back up only limited portions of your system. To do so, just name in your find command the directories you wish to back up. For example, to back up everything in your home directory and in /usr/lib, use the following command: 

     find $HOME /usr/lib -type f -newer cpio.daily -print | gnucpio -ocF /dev/rfha0
     touch cpio.daily

When you determine the backup strategy you wish to use, you should save the appropriate commands into a script, to ensure that backups are run correctly every time.

The following describes how to restore files from floppy disks.

If you find that a file has been inadvertently destroyed, you can restore the information to disk from backup floppy disks.

To restore information from backups created with gnucpio or tar, you must first determine the date and time that the file was last known to have been modified. From this date, determine on which set of disks the file was last correctly dumped. Find the set of floppy disks labeled with that date, and insert into the floppy-disk drive the first one in the set. For example, if you wish to restore the file myfile, from a gnucpio archive, use the command: 

     gnucpio -icdvF /dev/rfha0 myfile

To retrieve myfile from a tar archive, use the command: 

     tar xvf /dev/rfha0 myfile

Both of these commands assume that the disks are high- density, 5.25-inch floppies in drive 0 (drive A). See the Lexicon article floppy disk for a table that shows which COHERENT device is associated with which size and density of disk, and which disk drive. You may have to insert more than one disk from the set of backups until you find the one that holds the file you want.

Backing up Onto Tapes

The strategy for backing up onto tape resembles that for floppy disks, with the exception that in many instances the tape medium is larger than the device being backed up. This makes it worth your while to back up the entire device every time you do a back up, rather than perform incremental backups. The reason for this is simple: the fewer tapes over which you have spread your backups, the lower the risk that one will fail.

To back up an entire partition, do the following:

11..
Pop a tape into your tape device. Make sure the tape is appropriately labeled.

22..
Log in as the superuser root, and type the following command: 
     /etc/shutdown single 0

This returns your system to single-user mode immediately.

33..
Use the command gtar to back up your partition, as follows: 
     gtar -cvzf /dev/_t_a_p_e _d_i_r_e_c_t_o_r_y

tape identifies the tape device onto which the backup will be written, and directory identifies the file system to back up. For example, tape device /dev/rStp2 is a SCSI tape device that has SCSI identifier 2 and performs autorewinding. For a list of recognized tape devices, see the article for tape. in the Lexicon.

Please note two points about directory. First, do not use the absolute path name when specifying a directory: that is, use usr, not /usr. gtar strips the leading `/' in any event, but it's always best to use relative path names whenever possible. Second, in single-user mode only the root file system is mounted by default; therefore, if the file system you wish to back up resides on its own partition, you must mount that file system by hand before you begin to back it up.

Note that the z option to the gtar command tells gtar to use gzip to compress the files automatically. File compression is a good idea: because fewer bits are being written to the tape, the backup will go faster; and because less tape is used, the risk of a tape failure is lessened.

33..
When gtar has finished writing to the tape, wait until the tape finishes rewinding; then remove it from its drive and put it in a safe place (i.e., away from magnets and children). Then type <ctrl- D> to return your system to multi-user mode.

That's all there is to it. To restore information from the tape, put the tape into the drive and use the gtar command to fetch the file you want. For example, to restore file /v/fwb/myfile.c from a SCSI tape drive that has SCSI identifier 2, use the following command: 
     gtar -xvzf /dev/rStp2 "v/fwb/myfile.c"

Note that the file will be written into a subdirectory of your current directory. For example, if your current directory is /v/fwb, then myfile.c will be restored into a file with the path name /v/fwb/v/fwb/myfile.c. This may be a little inconvenient, but is not nearly as inconvenient as having to create myfile.c by hand.

An Example of Using Floppy Tape

This section gives examples of how to use QIC-40/QIC-80 (``floppy tape'') to write archives to floppy tape, and read them back. It uses the commands tape, which manipulates the tape device; and gtar, which writes archives onto the physical tape, and reads them back.

Suppose you have a directory named dir1, which contains files you want to backup. To back up all files in that directory onto a tape, insert a tape cartridge into the drive, then type: 

     gtar -cvf /dev/ft dir1

To verify that the contents of the tape match the original files, run gtar again in verification (``diff'') mode: 

     gtar -df /dev/ft

We strongly urge you to verify tapes after they have been written, especially with floppy-tape devices. If a tape fails this test, throw it away and build a new archive; otherwise, you may receive a nasty surprise when you try to restore a file from that tape. Do not be surprised if an otherwise sound tape fails after time: a tape does wear out after a number of uses.

To later extract the files from the tape, use 

     gtar -xf /dev/ft

To use data compression, the preceding commands can be used with the addition of gtar's option -z, as follows: 

     gtar -czvf /dev/ft dir1
     gtar -dzf /dev/ft
     gtar -xzf /dev/ft

To backup only selected files to tape, you could do the following: 

     find dir -type f -print | sort > Files

then manually edit the file Files so it contains only the names of the files you want to back up. Then use the command: 

     gtar -cv -T Files -f /dev/ft

The previous examples used /dev/ft, the device node that calls for the tape to be rewound when the device is closed. This is convenient if you are putting only one archive onto tape. To concatenate multiple archives on a single cartridge, use the no-rewind-on-close device. For example, suppose you have a second directory, dir2, and you want to back it up on the same tape, after an archive of dir1. The following commands accomplish this: 

     gtar -cvf /dev/nft dir1
     gtar -cvf /dev/nft dir2

After each archive is written, the tape remains positioned at the end of the archive. To verify the contents of both archives, do the following: 

     # this command rewinds the tape:
     tape rewind
     # this command displays the contents of the first archive:
     gtar -tvf /dev/nft
     # this command displays the contents of the second archive:
     gtar -tvf /dev/nft

If you make a note of the locations of archives as they are written, you can retrieve them later without having to read the preceding archives. For example: 

     # rewind the tape:
     tape rewind
     # write "dir1" archive at start of tape:
     gtar -cvf /dev/nft dir1
     # find current position of the tape:
     tape tell

The command tape tell returns a string of the form: 

     Tape Is at Byte Offset 102400

Continuing: 

     # write "dir2" archive after "dir1":
     gtar -cvf /dev/nft dir2
     # read the current position:
     tape tell

The second instance of tape tell returns a string of the form: 

     Tape Is at Byte Offset 235520

That is, it shows that the tape has advanced after the second archive was written onto it. At this point, the cartridge is removed, then reinserted into the tape drive at a later date: 

     tape seek 102400
     gtar -tvf /dev/tape

The command tape seek moves the tape to the byte position 102400, i.e., the end of the first archive. This command assumes that you jotted down the position displayed by the command tape tell executed earlier. The command gtar then displays the contents of the second archive.

See Also