User Manual

1.1 · What partmgr is

EFI Partition Manager is a program for UEFI firmware that shows, creates and changes partition tables, GPT and MBR, before any operating system has started. It is one file, partmgr.efi, started from the firmware boot menu or from a UEFI shell.

A disk is divided into partitions, and a small table at its beginning — the partition table — says where each partition starts, how big it is and what it is for. Preparing a disk for a new system, a recovery stick or a second drive starts with that table, and usually means booting a whole Linux or Windows environment just to run a partitioning tool. partmgr does it directly in the firmware.

What it offers:

• GPT and MBR, read and written in full: MBR with primary, extended and logical partitions, the active flag and the CHS fields.
• See first, write later: changes are made on the screen; the disk changes only when you choose Write and confirm.
• Backup and restore: the partition table of a disk saved to a file, and written back exactly as it was.
• Wipe: a partition overwritten twice, random data then zeros, with a progress bar and the time left.
• Safe by design: the disk partmgr was started from is never written; damaged tables are recognised and explained.
• Readable: types chosen from a list, sizes such as 512M or rest, no codes to remember.
• A window and the mouse: a graphical window used with the mouse or the keyboard; text screens where the firmware has no graphics.
• Its own code: written from scratch, with its own UEFI definitions, in one file.

1.2 · What partmgr does not do

partmgr works on partition tables. It does not format partitions (the firmware or the operating system does that), does not resize or move them, and does not install boot code. Deleting a partition removes it from the table; its data stays on the disk until something overwrites it.

The one thing partmgr writes inside a partition is a wipe, and only when asked: it overwrites the whole partition so that its data is gone.

1.3 · Who this manual is for

partmgr is made for people who know what a partition table is and how to reach a UEFI shell or the firmware boot menu. The window is therefore terse: short questions, fields with just a label, no explanations. The explanations are in this manual. What partmgr never drops is the confirmation of every operation that writes to a disk.

How partmgr is built and tested is in the technical manual.

1.4 · Conventions

2.1 · Requirements

2.2 · Getting partmgr.efi

Ready-made, partmgr.efi is on the release page of the project, with its checksum in SHA256SUMS.

1. Download partmgr.efi and SHA256SUMS from the release page.
2. Check the download: sha256sum -c SHA256SUMS.

To build it yourself, on Linux:

git clone https://github.com/nic-fio/EFI_PARTITION_MANAGER.git
cd EFI_PARTITION_MANAGER
make
ls -l build/partmgr.efi

The build needs gcc, GNU ld, make and python3; the technical manual has the details and the tests.

2.3 · Putting it on a stick

Copy partmgr.efi to a FAT-formatted stick. Two common layouts:

2.4 · Starting and leaving partmgr

1. From the firmware boot menu — usually opened with F12, F11, F8 or Esc during power-on — choose the stick. From a UEFI shell, type the file with its volume and folder.
2. partmgr opens the window when the firmware has a graphics screen of at least 640 × 480, and the text screens otherwise. In the window it opens the first disk it may change.
3. To leave, press Esc or click Quit; in the text screens, Q or Esc on the list of disks. If the disk shown has changes that are not written, partmgr asks first.

fs0:\> fs0:\EFI\tools\partmgr.efi

When you leave, the screen is cleared and you are back where you started partmgr from: the shell, with its cursor, or the firmware, which goes on with its boot order or its setup menu.

2.5 · Secure Boot

With Secure Boot active the firmware starts only signed programs. partmgr.efi is a file of its own, so it needs a signature with a key the machine trusts.

With your own keys, on Linux (package sbsigntool):

sbsign --key db.key --cert db.crt --output partmgr-signed.efi build/partmgr.efi
sbverify --cert db.crt partmgr-signed.efi

The certificate must be in the firmware's db database (enrolled from the firmware setup), or — on machines that boot through shim — in the MOK list (mokutil --import db.der). Otherwise, disable Secure Boot in the firmware setup while you use partmgr.

3.1 · The parts of the window

partmgr shows everything in one window, used with the mouse or with the keyboard. Where the firmware has no graphics screen it shows text screens instead, with the same keys.

The bar

One coloured block per partition, to scale: EFI system orange, Linux green, swap red, Microsoft, Windows, FAT and NTFS blue, anything else lilac. The free space is hatched grey. On an MBR disk the extended partition is a beige band behind its logical partitions. Each block carries its number and type, or only the number, or nothing, as room allows, and its size below when it fits. The selected row has a blue frame in the bar.

Names and marks of the disks

• Names. Disks are called blkN, where N counts every block device of the firmware, partitions included — which is why the numbers are not consecutive. They stay the same from one start to the next as long as the hardware does not change.
• started from here: read only marks the disk partmgr was loaded from. It can be looked at and backed up, never changed: changing the table under the running program could destroy it.
• write-protected marks a medium the firmware reports as read-only.
• no table: the disk has no partition table — new, erased, or with a file system written directly on the whole disk. unreadable: the firmware could not read it.
• A star after the number of partitions, and * = changes not written in the title bar, say that the selected disk has changes that are not written yet.

3.2 · Mouse and keys

Everything can be done with the mouse and everything with the keyboard; the two can be mixed.

Tab moves the arrow keys between the table of the disk and the list of disks: the one they move in has its selection in strong blue, the other in pale blue. Page Up and Page Down change the disk at any time. The button under the mouse pointer is highlighted. In the bar, a click on a logical partition selects it; the extended partition itself is selected in the table.

The mouse

partmgr uses the firmware's mouse when the firmware has one; when it has not — many do not — partmgr drives a USB mouse itself, through the simple boot protocol that USB mice offer. Tablets, touch screens and PS/2 mice work only when the firmware supports them. Without a mouse the pointer is not shown, and the keyboard does everything.

qemu-system-x86_64 -bios OVMF.fd ... -usb -device usb-mouse
qemu-system-x86_64 -machine q35 -bios OVMF.fd ... -device qemu-xhci -device usb-mouse

Leaving a disk that has changes not written — opening another disk, F5, Esc — asks Discard the unwritten changes? (Y/N) first (see section 7.3).

3.3 · The table of a disk

The table lists the partitions and the free areas, in the order they have on the disk.

Free areas appear in grey: free space, or on an MBR disk free space (for logical partitions) when the area is inside the extended partition. Only areas of at least 1 MiB are shown, starting on a 1 MiB boundary. Changed rows are amber, with their star. A disk without a table shows No partition table.

Under the table, Note: lines explain anything unusual partmgr found in the table (see section 10.3).

A key that does not apply

Every button is always there. One that does not apply to the selected row says why in one short line:

3.4 · Dialogs

Questions appear in a box over the window, which is dimmed meanwhile. A box with a red title asks before something that destroys data. The buttons show their keys.

3.5 · Screen sizes

partmgr keeps the resolution the firmware set — usually the monitor's own — and fits the window to it, from 640 × 480 up. The text grows with the height of the screen, in the same proportion on a 1080-row and on a 2160-row (4K) monitor; on a very large screen the pointer is twice as large. On a narrow screen the list of disks is narrower, the buttons lose their group names and get narrower, and take more rows if they must.

3.6 · The text screens

Where the firmware has no graphics screen of at least 640 × 480 — a server reached only through a serial console, for example — partmgr shows two text screens instead: the list of disks, and the screen of one disk. They do the same things with the same keys, answer with the same messages and ask the same questions.

In the text screens a message box closes with any key (Press a key.), a field shows Enter OK Esc Cancel and a list Enter Choose Esc Cancel. When the firmware offers a text mode of 100 columns or more, partmgr switches to the narrowest such mode, for the largest characters, and puts the previous mode back when it ends; at 80 columns the key bars are drawn narrower.

4.1 · The path

A session with partmgr always follows the same order: look, keep a copy, change on the screen, write.

1. Start partmgr from a stick (section 2.4) and pick the disk on the left.
2. Look at the table and at any Note: under it. Looking never writes anything.
3. Keep a copy of the table with B if the disk matters (section 8.1).
4. Change the table on the screen: N, D, T, Z… Every change is marked with a star.
5. Write with Enter, and answer Y to the red question (section 7.1).

4.2 · Preparing a new stick

An example from start to end: a stick for UEFI systems with an EFI system partition of 512 MiB and a Linux partition on the rest.

1. Select the stick in the list of disks. Check its name, kind and size twice: everything on it will go.
2. Press Z (New table), choose GPT. The message line says New empty GPT table. and the table shows one free area.
3. With the free area selected, press N. The start proposed is 1 MiB: press Enter. For the size type 512M and Enter. Choose EFI system in the list, type a name if you want one, Enter. The message line says Partition 1 added.
4. Select the free area after it and press N again: Enter for the start, Enter for the size (rest, all the free space), Linux filesystem, a name, Enter.
5. Press Enter (Write). The question reads Write the GPT table to blkN (…)? (Y/N): press Y. The message line says Written. and the stars are gone.

4.3 · Changing your mind

Until Write, nothing has reached the disk. To throw the changes away, open another disk, press F5 or leave partmgr, and answer Y to Discard the unwritten changes? (Y/N). F5 reads the disks again and shows the same disk as it is on the disk.

5.1 · GPT

The GUID Partition Table is the table of UEFI.

It holds up to 128 partitions (more on some disks; a new table made by partmgr has 128 entries), each with a type and an identifier written as a GUID, and a name. It is kept twice: at the beginning of the disk and, as a backup, at the end, each copy with a checksum. Block 0 keeps a protective MBR that tells old tools the disk is in use. Disks of any size are fine.

5.2 · MBR

The Master Boot Record is the older table, in block 0 only.

It holds four entries. To have more partitions, one entry is an extended partition, a container for any number of logical partitions, each described by a small table of its own chained to the next. The active flag marks the partition old BIOS systems start. An MBR addresses at most 2 TiB (with the usual 512-byte blocks).

5.3 · Alignment

partmgr starts partitions on 1 MiB boundaries, as current systems do: it is good for SSDs and for disks with 4096-byte sectors. A start you type is rounded up to the next MiB. On an MBR disk each logical partition needs one block before it for its table, so a free area inside the extended partition starts 1 MiB after the partition before it.

6.1 · New partition

Select a free area and press N — or click New. partmgr asks, one at a time:

1. On an MBR disk, primary or logical — only when the disk has no extended partition yet: Primary or Logical (creates the extended partition). A logical partition creates the extended partition over the whole free area. In a free area inside the extended partition the new partition is logical without asking.
2. Start, proposed as the beginning of the free area; the dialog says where the free area begins and ends (Start (free: 317 MiB to 511.9 MiB):). Enter accepts it; typing replaces it. The start must lie in the free area. A logical partition that creates the extended one starts 1 MiB into the area: that first MiB holds the table of the chain.

3. Size, proposed as rest: all the free space after the start, whose amount the dialog shows. Or type a size: 512M, 20G, 1.5T (see section 12.2). If it does not fit, partmgr says how much does.
4. Type, chosen from a list with a click, or with the arrows and Enter. Other (type GUID)... at the end takes a type GUID on a GPT disk, Other (type byte)... a type byte in hexadecimal on an MBR disk. See section 12.3.
5. Name, on GPT only: up to 36 characters, or empty.

The message line then says Partition N added. Esc at any step cancels the new partition. On an MBR disk the logical partitions are numbered in disk order, so adding one in front of others renumbers them (and marks them with a star). What partmgr answers when a value does not fit is in section 11.1.

6.2 · Delete a partition

Select it and press D. The partition disappears from the table and its space becomes free: Partition N deleted. Deleting the extended partition deletes its logical partitions too; partmgr asks first when there are any: Delete the extended partition and its 2 logical partitions? (Y/N).

6.3 · Change the type

T opens the list of types with the current one selected; the message line then says Partition N: type changed. The extended partition keeps its type (The extended partition keeps its type.), and no other partition can be given an extended type: extended partitions are made by adding logical ones.

6.4 · Rename (GPT)

R changes the name of a GPT partition: up to 36 characters, or empty (Partition N renamed.). MBR partitions have no names.

6.5 · Active flag (MBR)

A makes the selected partition the active one (Partition N active.), or takes the flag away if it has it (Partition N no longer active.). Only one partition is active at a time: setting it moves it. The extended partition cannot be active. UEFI ignores the flag; old BIOS systems start the active partition.

6.6 · New partition table

Z replaces the table with a new, empty one: GPT or MBR, chosen from a list (New empty GPT table.). A new table is made from zero: every partition of the disk goes, the disk gets new identifiers, and block 0 has no boot code — boot code belongs to boot loaders, which install their own. Add partitions, then Write.

6.7 · Delete the partition table

X removes the table altogether (Partition table deleted.). After Write the disk looks empty to every system; the data of the partitions is not touched.

7.1 · Write

When the window shows the table you want, press Enter or click Write. partmgr asks, in red, one question.

For example Write the GPT table to blk3 (512.0 MiB)? (Y/N) — or, after X, Delete the partition table of blk3 (512.0 MiB)? (Y/N).

1. Press Y or click Yes: the table is written, read back from the disk and shown again, and the message line says Written.
2. Or press N, Esc or click No: nothing happens, and the message line says Nothing was written.

7.2 · What Write writes

Write never touches the data inside the partitions. If the disk refuses the write, a box says why and the message line reads Not written: ….

7.3 · Leaving without writing

Opening another disk, reading the disks again (F5) or leaving partmgr (Esc) with changes not written asks first, in red, Discard the unwritten changes? (Y/N): Y leaves them, N stays. In the text screens Esc goes back to the list of disks and asks the same. Leaving without writing leaves the disk exactly as it was.

8.1 · Backup

B saves the partition table as it is on the disk to a small file — changes on the screen that are not written yet are not in it.

1. Press B. partmgr proposes the file of the last backup or restore since it was started; the first time, a file on the volume it was started from, or on the first volume that can be written when that one cannot: fs1:\partmgr-blk7.bin.
2. The dialog lists the volumes, marking the read-only ones with (ro). Accept the name or type another path, always with its volume (fs1:\backups\disk.bin; the folder must exist).
3. If the file exists, partmgr asks The file exists. Replace it? (Y/N).
4. The message line says Saved fs1:\partmgr-blk7.bin (512 bytes).

A backup is small: one or a few kilobytes for an MBR, about 34 KB for a GPT on a disk with 512-byte blocks. It holds the blocks of the table exactly as they are on the disk — block 0 and the tables of the logical partitions for an MBR; the protective MBR and both GPT copies for a GPT — with the size of the disk and a checksum. It does not hold any data of the partitions. A backup can be made of every disk, the read-only ones included; a disk without a table has nothing to back up.

8.2 · Restore

S writes a backup back to the disk.

1. Press S. partmgr proposes the file of the last backup or restore since it was started; type another path if needed.
2. partmgr reads the file and asks, in red, Restore fs1:\partmgr-blk7.bin to blk7? (Y/N) — with Unwritten changes are lost. added when there are some.
3. After Y it checks the file before writing anything: it must be a partmgr backup, undamaged, made on a disk of the same size and block size. Then the table is written and read back: Restored from fs1:\partmgr-blk7.bin.

Why a file can be refused is in section 11.2.

8.3 · A safe routine

1. Before changing a disk that matters: B to a stick.
2. Make the changes, then Write.
3. If the result is not what you wanted, S brings the old table back — and with it every partition that was there, since their data was never touched.

9.1 · Wipe

Destroying the data of one partition, when the disk goes to someone else or the data must not come back.

Select the partition and press W. partmgr asks, in red, with the partition's number, type, size and name: Wipe partition 3 of blk3 (Linux filesystem, 1.0 GiB, "Linux root")? (Y/N). The wipe then starts at once: it is not a change of the table, so it does not wait for Write.

It makes two passes over every block of the partition: first random data, then zeros. The random pass leaves nothing of the old contents; the zeros make the partition read as empty to every tool afterwards, with no trace of the old file system. The partition stays in the table with its type and name: only its contents are gone.

9.2 · Progress, and stopping

While it runs, partmgr shows which pass it is in, a bar with the percentage of the pass, how much of the partition the pass has written, the speed, and the time left for both passes (estimating the time... for the first half second). A large disk takes time: at 150 MiB/s, a 1 TiB partition takes about four hours for the two passes.

Esc, or a click on Stop, asks Stop the wipe? (Y/N). Stopping leaves the partition partly overwritten — its old data is damaged either way — and the message line says in which pass it stopped: Wipe of partition 3 stopped in pass 1: partly overwritten. At the end the message line says how much was overwritten and how long it took: Partition 3 wiped (1.0 GiB, 2 passes, 38 s).

9.3 · What can be wiped

9.4 · SSDs, NVMe drives and USB sticks

The complete way to clear a flash drive is its own erase command (ATA Secure Erase, NVMe Sanitize or Format), which works on the whole drive, never on one partition, and which partmgr does not issue.

10.1 · Disks that are only shown

The disk partmgr was started from, and write-protected disks, can be opened and backed up, but every change is refused with a box titled Read only:

• partmgr was started from this disk: it cannot be changed.
• The disk is write-protected.

There is no way around it. To change the disk partmgr runs from, start partmgr from another stick.

10.2 · Limits

10.3 · What the notes mean

When the table of a disk is unusual or damaged, partmgr shows it as well as it can and explains below the table with Note: lines. Write then writes a clean table — which is also how most of these are repaired.

11.1 · Messages when adding a partition

They appear in a box titled New partition; nothing has changed, and N starts again.

11.2 · Messages of the other actions

11.3 · Frequent problems

11.4 · Reporting how partmgr behaved

partmgr is tested in QEMU with OVMF and on disk images checked by other partitioning tools; reports from real machines are the most useful help. Open a hardware report on the project page, with the machine, the firmware, the version shown in the title bar and, if you can, a photograph of the window.

12.1 · Keys

Every key of the window has a button showing it; a click on the button does the same.

In the text screens: on the list of disks Enter opens a disk, R reads the disks again and Q or Esc leave; on the screen of a disk the keys above, and Esc back to the list. In a dialog, see section 3.4.

12.2 · Writing sizes

A size that is not a whole number of blocks is rounded down; a start is rounded up to the next MiB.

12.3 · Partition types

The lists, in the order partmgr shows them (the MBR table reads down its first column, then the second). Other types are entered with Other…, and a type partmgr has no name for is shown as its GUID or byte.

The extended types (05, 0F, 85) and the GPT protective type (EE) are recognised but never chosen by hand: partmgr creates the extended partition itself, with 05, or 0F when it reaches beyond 8 GB.

13.1 · Terms

Active partition

On an MBR disk, the partition an old BIOS starts. UEFI ignores it. See section 6.5.

Block

The unit a disk is read and written in: 512 or 4096 bytes. Also called a sector.

Boot code

The small program at the start of an MBR, written by a boot loader for BIOS systems. partmgr keeps it when changing a table and leaves it empty in a new one.

EFI system partition

The FAT partition UEFI firmware starts boot loaders from.

Extended boot record

The small table in front of each logical partition, chained to the next one.

Extended partition

On an MBR disk, the container of the logical partitions. See section 5.2.

GPT

GUID Partition Table, the partition table of UEFI. See section 5.1.

GUID

A 128-bit identifier, written C12A7328-F81F-11D2-BA4B-00A0C93EC93B.

Hybrid MBR

A GPT disk whose block 0 also describes some partitions for legacy systems. partmgr leaves it as it is.

MBR

Master Boot Record, the partition table of the PC BIOS, in block 0. See section 5.2.

Partition

A part of a disk, described in the partition table, usually holding one file system.

Protective MBR

Block 0 of a GPT disk: one entry covering the disk, so that old tools see it is in use.

Superfloppy

A disk formatted as a whole, with no partition table.

Wipe

To overwrite the contents of a partition so that its data is gone. Not the same as deleting it. See chapter 9.