slow startup of calibre on macos 15.7.5

jordi · 04-25-2026, 03:48 PM

I've configured calibre 9.7 on MacOS Sequoia for the first time to hold my library of 428 books/journals (30 GB).
I wonder, why calibre takes more than a minute to startup. Even with a much smaller library, the startup time stays that long...

Here ist my debug output, which shows that a huge amount of time is taken during the "Constructing main UI..." phase:

macOS-15.7.5-arm64-arm-64bit-Mach-O Darwin ('64bit', 'Mach-O')
('Darwin', '24.6.0', 'Darwin Kernel Version 24.6.0: Fri Feb 27 19:34:42 PST 2026; root:xnu-11417.140.69.709.8~1/RELEASE_ARM64_T6020')
Python 3.14.2
OSX: ('15.7.5', ('', '', ''), 'arm64')
Interface language: de
EXE path: /Applications/calibre.app/Contents/MacOS/calibre-debug
QPA platform: cocoa
devicePixelRatio: 2.0
logicalDpi: 72.0 x 72.0
physicalDpi: 108.50000162950651 x 107.50000161448803
ApplicationPaletteChange event ignored
Using calibre Qt style: True
[0.00] Starting up...
[0.02] Showing splash screen...
[1.19] splash screen shown
[1.19] Initializing db...
[1.20] db initialized
[1.20] Constructing main UI...
[76.52] GUI main window shown
[76.56] main UI initialized...
[76.56] Hiding splash screen
[76.60] splash screen hidden
[76.60] Started up in 76.60 seconds with 428 books

Thanks for any ideas!

theducks · 04-25-2026, 07:27 PM

Not a Mac person, but the usual culprits are overly aggressive A/V or low system resources. 500 books is nothing (the books do not load, only the DB) compared to many Calibre Libraries

kovidgoyal · 04-25-2026, 11:34 PM

The delay is not in loading the books, according to your log that is taking 0.01 seconds. The delay is in constructing the window, which means likely something on your machine is interfering with calibre. Not a mac user so cant tell you what that might be but I would start by disabling any assistive technologies like VoiceOver and similar these tend to not play well with Qt the toolkit calibre uses.

jordi · 05-01-2026, 07:32 PM

Thank's a lot!

The long startup time is likely caused by the Synology Drive Client app, which also uses the Qt toolkit and interferes with calibre.

Within the first few minutes after restarting the Mac, everything is still fine; however, after that, the startup phase of Calibre takes more than a minute.

My current workaround is to run calibre in a Parallels VM...

jordi · 05-02-2026, 08:41 AM

I've investigated the issue a little bit further:

After starting calibre with the "DYLD_PRINT_LIBRARIES=1" parameter I figured out, that calibre stops for a quite amount of time when the System Library extension IOUSBLib is loaded.

I'm running MacOS with no external readers connected. So I've tried to disable all Calibre mtp plugins, but that doesn't changed anything.

So instead I've removed the libusb.so plugin from calibre and now it works...

Does calibre scan for an external device on startup and is there a timeout for about 70 sec. that has to be passed, before the startup process continues?

And is there another way to avoid this devices scan?

serrnovik · 05-02-2026, 05:51 PM

I guess i have same issue but worse.

I have ~47k books in my Calibre library.

On my MacBook M4, Calibre grows to eating 130+GB of memory, then the system reports that OS has no memory, and I can only kill it.
The library is on USB SSD drive. The same library opens on Windows just fine on the current version of Calibre.

What I’ve tried:
- Starting with no plugins
- Clearing all cache
- Wiping out anything related to Calibre and reinstalling from scratch
- Installing with the installer and not brew
- Going back a few versions
- Killing metadata.db (then calibre starts) and rebuilding DB from files (once Calibre opens after rebuild, it crashes again)

So no matter what I do, it crashes on 'Constructing main UI'. Even on a clean install and no plugins. Even after working before restoring from a database backup.

Again, the same library works in any way fine on Windows. The same library worked on the same Mac a few weeks ago (not sure exactly when).

/Applications/calibre.app/Contents/MacOS/calibre-debug -g -- --ignore-plugins --with-library "/Volumes/SamsungT5sn/NAMEOFALIBRARY"
calibre 9.8 embedded-python: True
macOS-26.4.1-arm64-arm-64bit-Mach-O Darwin ('64bit', 'Mach-O')
('Darwin', '25.4.0', 'Darwin Kernel Version 25.4.0: Thu Mar 19 19:33:25 PDT 2026; root:xnu-12377.101.15~1/RELEASE_ARM64_T6041')
Python 3.14.4
OSX: ('26.4.1', ('', '', ''), 'arm64')
Interface language: None
EXE path: /Applications/calibre.app/Contents/MacOS/calibre-debug
Using library at /Volumes/SamsungT5sn/NAMEOFALIBRARY
QPA platform: cocoa
devicePixelRatio: 2.0
logicalDpi: 72.0 x 72.0
physicalDpi: 151.50000227530174 x 151.50000227530174
ApplicationPaletteChange event ignored
Using calibre Qt style: True
[0.00] Starting up...
[0.04] Showing splash screen...
[1.21] splash screen shown
[1.21] Initializing db...
[1.68] db initialized
[1.68] Constructing main UI...
zsh: killed /Applications/calibre.app/Contents/MacOS/calibre-debug -g -- --ignore-plugins

serrnovik · 05-02-2026, 06:07 PM

Followup: in previous post suspicion was about libusb

following didn't help.
# Rename them so Calibre can't load them
mv libusb.so libusb.so.disabled 2>/dev/null
mv libmtp.so libmtp.so.disabled 2>/dev/null
mv usbobserver.so usbobserver.so.disabled 2>/dev/null

removing USB and MTP plugins didn’t help.

kovidgoyal · 05-02-2026, 09:06 PM

Quote:

Originally Posted by jordi

Does calibre scan for an external device on startup and is there a timeout for about 70 sec. that has to be passed, before the startup process continues?

And is there another way to avoid this devices scan?

Device scanning happens in its own thread and no you cannot avoid it.

serrnovik · 05-03-2026, 05:48 AM

Any way to avoid memory leaks? Actually really possible that this arrived after OS update.

jordi · 05-03-2026, 07:18 AM

Quote:

Originally Posted by kovidgoyal

Device scanning happens in its own thread and no you cannot avoid it.

but maybe in calibre Version 9.9.0

kovidgoyal · 05-03-2026, 07:34 AM

Quote:

Originally Posted by jordi

but maybe in calibre Version 9.9.0

No, I'm afraid not. This issue is specific to something on your machine.

kovidgoyal · 05-03-2026, 07:36 AM

Quote:

Originally Posted by serrnovik

Any way to avoid memory leaks? Actually really possible that this arrived after OS update.

It isnt a leak coming form a calibre component so no idea. Also I should note that sharing a library folder between windows and macos is not a good idea, you will end up with data loss because those two have very different filesystem semantics.

jordi · 05-03-2026, 07:43 AM

Quote:

Originally Posted by serrnovik

I guess i have same issue but worse.

I have ~47k books in my Calibre library.

Your's seems to be more severe, because mine doesn't crash but just takes a little bit longer to load

Have you tried to figure out, which shared libraries are successfully loaded and when calibre stops?

Code:

DYLD_PRINT_LIBRARIES=1 /Applications/calibre.app/Contents/MacOS/calibre 2> loaded_libraries.txt

Not a real trace but maybe a hint...

jordi · 05-03-2026, 07:51 AM

Quote:

Originally Posted by kovidgoyal

No, I'm afraid not. This issue is specific to something on your machine.

understood!

Do you think, one of the USB device drivers on my machine makes calibre's device scanning process pause for a certain amount of time?

serrnovik · 05-03-2026, 09:06 AM

Actually now i understand even less. Direct execution of`/Applications/calibre.app/Contents/MacOS/calibre` now suddenly works. Even with all plugins, etc.

BUT running from Dock or just click ok 'restart' calibre goes to memory leak.

/Applications/calibre.app/Contents/MacOS/calibre --with-library "/Volumes/SamsungT5sn/MYLIB" took 25s
Using library at /Volumes/SamsungT5sn/MYLIB

So i don't know if this is my system or what. But i'll guess i'll just stick to the command line start temporarily.

---
regarding USB device lib
dyld[53335]: <C253982B-BED7-3329-9694-6380DC587E0C> /Applications/calibre.app/Contents/Frameworks/plugins/usbobserver.so
it is there. Otherwise output is huge. is there anything to look for?

...
dyld[53335]: <70FD96D1-6C8F-3995-9957-DD33F4241B68> /Applications/calibre.app/Contents/Frameworks/plugins/binascii.so
dyld[53335]: <67195A61-7207-339A-8815-598B64DD76D7> /Applications/calibre.app/Contents/Frameworks/plugins/_hashlib.so
dyld[53335]: <607B6EBF-88D4-347B-84D8-1DC172F4E610> /Applications/calibre.app/Contents/Frameworks/libcrypto.3.dylib
dyld[53335]: <67EA3700-6545-3FBB-9726-746A4BE20758> /Applications/calibre.app/Contents/Frameworks/plugins/_blake2.so
dyld[53335]: <3FBFDCAA-4868-3F78-933F-93EB483AAEE4> /Applications/calibre.app/Contents/Frameworks/plugins/_ssl.so
dyld[53335]: <81684FD3-13EE-37C9-BEFE-43D69CCB037C> /Applications/calibre.app/Contents/Frameworks/libssl.3.dylib
dyld[53335]: <9704B773-BA0B-3DF1-A9F1-6572CBC26E48> /Applications/calibre.app/Contents/Frameworks/plugins/_scproxy.so
dyld[53335]: <5B5F83BB-0782-366E-ABE0-1E1DBC52D91C> /Applications/calibre.app/Contents/Frameworks/plugins/_zoneinfo.so
dyld[53335]: <1ADFC14F-5F8E-3F1E-9421-22C8805269E5> /Applications/calibre.app/Contents/Frameworks/plugins/speedup.so
dyld[53335]: <05D4F376-DF1D-3935-9B1D-3A8E2C9D787D> /Applications/calibre.app/Contents/Frameworks/plugins/grp.so
dyld[53335]: <C253982B-BED7-3329-9694-6380DC587E0C> /Applications/calibre.app/Contents/Frameworks/plugins/usbobserver.so
dyld[53335]: <436BB073-C40B-3067-A702-AE21EB293743> /Applications/calibre.app/Contents/Frameworks/plugins/imageops.so
dyld[53335]: <0BE5A9E7-0E07-3AC9-8B8B-D770085A8562> /Applications/calibre.app/Contents/Frameworks/plugins/apsw.__init__.so
dyld[53335]: <99B8CA53-0033-3451-BAEF-4CFD74F3890D> /Applications/calibre.app/Contents/Frameworks/libsqlite3.dylib
Usage: calibre [options] [path_to_ebook or calibre url ...]

Launch the main calibre Graphical User Interface and optionally add the e-book at
path_to_ebook to the database. You can also specify calibre URLs to perform various
different actions, than just adding books. For example:

calibre://view-book/test_library/1842/epub

Will open the book with id 1842 in the EPUB format from the library
"test_library" in the calibre E-book viewer. Library names are the folder names of the
libraries with spaces replaced by underscores. A full description of the
various URL based actions is in the User Manual.

Whenever you pass arguments to calibre that have spaces in them, enclose the arguments in quotation marks. For example: "/some path/with spaces"

04-25-2026, 03:48 PM	#1
jordi Junior Member Posts: 9 Karma: 10 Join Date: Apr 2026 Device: iPad	slow startup of calibre on macos 15.7.5 I've configured calibre 9.7 on MacOS Sequoia for the first time to hold my library of 428 books/journals (30 GB). I wonder, why calibre takes more than a minute to startup. Even with a much smaller library, the startup time stays that long... Here ist my debug output, which shows that a huge amount of time is taken during the "Constructing main UI..." phase: macOS-15.7.5-arm64-arm-64bit-Mach-O Darwin ('64bit', 'Mach-O') ('Darwin', '24.6.0', 'Darwin Kernel Version 24.6.0: Fri Feb 27 19:34:42 PST 2026; root:xnu-11417.140.69.709.8~1/RELEASE_ARM64_T6020') Python 3.14.2 OSX: ('15.7.5', ('', '', ''), 'arm64') Interface language: de EXE path: /Applications/calibre.app/Contents/MacOS/calibre-debug QPA platform: cocoa devicePixelRatio: 2.0 logicalDpi: 72.0 x 72.0 physicalDpi: 108.50000162950651 x 107.50000161448803 ApplicationPaletteChange event ignored Using calibre Qt style: True [0.00] Starting up... [0.02] Showing splash screen... [1.19] splash screen shown [1.19] Initializing db... [1.20] db initialized [1.20] Constructing main UI... [76.52] GUI main window shown [76.56] main UI initialized... [76.56] Hiding splash screen [76.60] splash screen hidden [76.60] Started up in 76.60 seconds with 428 books Thanks for any ideas!

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04-25-2026, 07:27 PM	#2
theducks Well trained by Cats Posts: 31,782 Karma: 64144480 Join Date: Aug 2009 Location: The Central Coast of California Device: Kobo Libra2,Kobo Aura2v1, K4NT(Fixed: New Bat.), Galaxy Tab A	Not a Mac person, but the usual culprits are overly aggressive A/V or low system resources. 500 books is nothing (the books do not load, only the DB) compared to many Calibre Libraries

04-25-2026, 11:34 PM	#3
kovidgoyal creator of calibre Posts: 46,256 Karma: 29630732 Join Date: Oct 2006 Location: Mumbai, India Device: Various	The delay is not in loading the books, according to your log that is taking 0.01 seconds. The delay is in constructing the window, which means likely something on your machine is interfering with calibre. Not a mac user so cant tell you what that might be but I would start by disabling any assistive technologies like VoiceOver and similar these tend to not play well with Qt the toolkit calibre uses.

05-01-2026, 07:32 PM	#4
jordi Junior Member Posts: 9 Karma: 10 Join Date: Apr 2026 Device: iPad	Thank's a lot! The long startup time is likely caused by the Synology Drive Client app, which also uses the Qt toolkit and interferes with calibre. Within the first few minutes after restarting the Mac, everything is still fine; however, after that, the startup phase of Calibre takes more than a minute. My current workaround is to run calibre in a Parallels VM...

05-02-2026, 08:41 AM	#5
jordi Junior Member Posts: 9 Karma: 10 Join Date: Apr 2026 Device: iPad	I've investigated the issue a little bit further: After starting calibre with the "DYLD_PRINT_LIBRARIES=1" parameter I figured out, that calibre stops for a quite amount of time when the System Library extension IOUSBLib is loaded. I'm running MacOS with no external readers connected. So I've tried to disable all Calibre mtp plugins, but that doesn't changed anything. So instead I've removed the libusb.so plugin from calibre and now it works... Does calibre scan for an external device on startup and is there a timeout for about 70 sec. that has to be passed, before the startup process continues? And is there another way to avoid this devices scan?

05-02-2026, 05:51 PM	#6
serrnovik Member Posts: 11 Karma: 57290 Join Date: Oct 2025 Device: ipad	I guess i have same issue but worse. I have ~47k books in my Calibre library. On my MacBook M4, Calibre grows to eating 130+GB of memory, then the system reports that OS has no memory, and I can only kill it. The library is on USB SSD drive. The same library opens on Windows just fine on the current version of Calibre. What I’ve tried: - Starting with no plugins - Clearing all cache - Wiping out anything related to Calibre and reinstalling from scratch - Installing with the installer and not brew - Going back a few versions - Killing metadata.db (then calibre starts) and rebuilding DB from files (once Calibre opens after rebuild, it crashes again) So no matter what I do, it crashes on 'Constructing main UI'. Even on a clean install and no plugins. Even after working before restoring from a database backup. Again, the same library works in any way fine on Windows. The same library worked on the same Mac a few weeks ago (not sure exactly when). /Applications/calibre.app/Contents/MacOS/calibre-debug -g -- --ignore-plugins --with-library "/Volumes/SamsungT5sn/NAMEOFALIBRARY" calibre 9.8 embedded-python: True macOS-26.4.1-arm64-arm-64bit-Mach-O Darwin ('64bit', 'Mach-O') ('Darwin', '25.4.0', 'Darwin Kernel Version 25.4.0: Thu Mar 19 19:33:25 PDT 2026; root:xnu-12377.101.15~1/RELEASE_ARM64_T6041') Python 3.14.4 OSX: ('26.4.1', ('', '', ''), 'arm64') Interface language: None EXE path: /Applications/calibre.app/Contents/MacOS/calibre-debug Using library at /Volumes/SamsungT5sn/NAMEOFALIBRARY QPA platform: cocoa devicePixelRatio: 2.0 logicalDpi: 72.0 x 72.0 physicalDpi: 151.50000227530174 x 151.50000227530174 ApplicationPaletteChange event ignored Using calibre Qt style: True [0.00] Starting up... [0.04] Showing splash screen... [1.21] splash screen shown [1.21] Initializing db... [1.68] db initialized [1.68] Constructing main UI... zsh: killed /Applications/calibre.app/Contents/MacOS/calibre-debug -g -- --ignore-plugins

05-02-2026, 06:07 PM	#7
serrnovik Member Posts: 11 Karma: 57290 Join Date: Oct 2025 Device: ipad	Followup: in previous post suspicion was about libusb following didn't help. # Rename them so Calibre can't load them mv libusb.so libusb.so.disabled 2>/dev/null mv libmtp.so libmtp.so.disabled 2>/dev/null mv usbobserver.so usbobserver.so.disabled 2>/dev/null removing USB and MTP plugins didn’t help.

05-03-2026, 05:48 AM	#9
serrnovik Member Posts: 11 Karma: 57290 Join Date: Oct 2025 Device: ipad	Any way to avoid memory leaks? Actually really possible that this arrived after OS update.

05-03-2026, 09:06 AM	#15
serrnovik Member Posts: 11 Karma: 57290 Join Date: Oct 2025 Device: ipad	Actually now i understand even less. Direct execution of`/Applications/calibre.app/Contents/MacOS/calibre` now suddenly works. Even with all plugins, etc. BUT running from Dock or just click ok 'restart' calibre goes to memory leak. /Applications/calibre.app/Contents/MacOS/calibre --with-library "/Volumes/SamsungT5sn/MYLIB" took 25s Using library at /Volumes/SamsungT5sn/MYLIB So i don't know if this is my system or what. But i'll guess i'll just stick to the command line start temporarily. --- regarding USB device lib dyld[53335]: <C253982B-BED7-3329-9694-6380DC587E0C> /Applications/calibre.app/Contents/Frameworks/plugins/usbobserver.so it is there. Otherwise output is huge. is there anything to look for? ... dyld[53335]: <70FD96D1-6C8F-3995-9957-DD33F4241B68> /Applications/calibre.app/Contents/Frameworks/plugins/binascii.so dyld[53335]: <67195A61-7207-339A-8815-598B64DD76D7> /Applications/calibre.app/Contents/Frameworks/plugins/_hashlib.so dyld[53335]: <607B6EBF-88D4-347B-84D8-1DC172F4E610> /Applications/calibre.app/Contents/Frameworks/libcrypto.3.dylib dyld[53335]: <67EA3700-6545-3FBB-9726-746A4BE20758> /Applications/calibre.app/Contents/Frameworks/plugins/_blake2.so dyld[53335]: <3FBFDCAA-4868-3F78-933F-93EB483AAEE4> /Applications/calibre.app/Contents/Frameworks/plugins/_ssl.so dyld[53335]: <81684FD3-13EE-37C9-BEFE-43D69CCB037C> /Applications/calibre.app/Contents/Frameworks/libssl.3.dylib dyld[53335]: <9704B773-BA0B-3DF1-A9F1-6572CBC26E48> /Applications/calibre.app/Contents/Frameworks/plugins/_scproxy.so dyld[53335]: <5B5F83BB-0782-366E-ABE0-1E1DBC52D91C> /Applications/calibre.app/Contents/Frameworks/plugins/_zoneinfo.so dyld[53335]: <1ADFC14F-5F8E-3F1E-9421-22C8805269E5> /Applications/calibre.app/Contents/Frameworks/plugins/speedup.so dyld[53335]: <05D4F376-DF1D-3935-9B1D-3A8E2C9D787D> /Applications/calibre.app/Contents/Frameworks/plugins/grp.so dyld[53335]: <C253982B-BED7-3329-9694-6380DC587E0C> /Applications/calibre.app/Contents/Frameworks/plugins/usbobserver.so dyld[53335]: <436BB073-C40B-3067-A702-AE21EB293743> /Applications/calibre.app/Contents/Frameworks/plugins/imageops.so dyld[53335]: <0BE5A9E7-0E07-3AC9-8B8B-D770085A8562> /Applications/calibre.app/Contents/Frameworks/plugins/apsw.__init__.so dyld[53335]: <99B8CA53-0033-3451-BAEF-4CFD74F3890D> /Applications/calibre.app/Contents/Frameworks/libsqlite3.dylib Usage: calibre [options] [path_to_ebook or calibre url ...] Launch the main calibre Graphical User Interface and optionally add the e-book at path_to_ebook to the database. You can also specify calibre URLs to perform various different actions, than just adding books. For example: calibre://view-book/test_library/1842/epub Will open the book with id 1842 in the EPUB format from the library "test_library" in the calibre E-book viewer. Library names are the folder names of the libraries with spaces replaced by underscores. A full description of the various URL based actions is in the User Manual. Whenever you pass arguments to calibre that have spaces in them, enclose the arguments in quotation marks. For example: "/some path/with spaces"