hexdump is a linux only tool #601

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adam · 2025-12-29T01:27:44+01:00

adam commented

2025-12-29 01:27:44 +01:00

Originally created by @drboone on GitHub (May 10, 2023).

The hexdump command is linux-only, and apparently comes from the util-linux command. Something that is available on other platforms would be a better choice. I haven't followed my way through the script to figure out where all it uses this, so I don't know what features and formats are required. I do know that dehydrated has been working flawlessly on my Illumos-derived systems for years without hexdump installed. Maybe xxd would work? That seems to be widely available.

Originally created by @drboone on GitHub (May 10, 2023). The hexdump command is linux-only, and apparently comes from the util-linux command. Something that is available on other platforms would be a better choice. I haven't followed my way through the script to figure out where all it uses this, so I don't know what features and formats are required. I do know that dehydrated has been working flawlessly on my Illumos-derived systems for years without hexdump installed. Maybe xxd would work? That seems to be widely available.

adam commented

2025-12-29 01:27:45 +01:00

@lukas2511 commented on GitHub (May 11, 2023):

Mh.. that's news to me. Hexdump also exists on MacOS and FreeBSD, and a lot of other systems, I'd also assume that it's available on Illumos and similar systems since I've heard about quite a few dehydrated users on those platforms, but since the use of hexdump is relatively new maybe nobody else ran into that issue yet.

For now it should only be used for EAB handling so it's not critical for most users, but dehydrated checks for its existence in any case, so if it's not available dehydrated will refuse to work. Since that also should only be important for registration I could at least move the check into that function so it doesn't disrupt any other operation..

Unfortunately xxd doesn't seem to exist in busybox systems while hexdump does, so I'd still prefer hexdump here. A solution without external tools would be ideal but I don't think that's possible with bash.

If you can suggest a replacement that's available everywhere and ideally pre-installed on even minimal systems I'd reconsider changing it, but for now I think I'll stay with hexdump and will consider moving the check to right before it's actually been required. Leaving this ticket open for now as a reminder.

@lukas2511 commented on GitHub (May 11, 2023): Mh.. that's news to me. Hexdump also exists on MacOS and FreeBSD, and a lot of other systems, I'd also assume that it's available on Illumos and similar systems since I've heard about quite a few dehydrated users on those platforms, but since the use of hexdump is relatively new maybe nobody else ran into that issue yet. For now it should only be used for EAB handling so it's not critical for most users, but dehydrated checks for its existence in any case, so if it's not available dehydrated will refuse to work. Since that also should only be important for registration I could at least move the check into that function so it doesn't disrupt any other operation.. Unfortunately `xxd` doesn't seem to exist in busybox systems while hexdump does, so I'd still prefer hexdump here. A solution without external tools would be ideal but I don't think that's possible with bash. If you can suggest a replacement that's available everywhere and ideally pre-installed on even minimal systems I'd reconsider changing it, but for now I think I'll stay with hexdump and will consider moving the check to right before it's actually been required. Leaving this ticket open for now as a reminder.

adam commented

2025-12-29 01:27:45 +01:00

@drboone commented on GitHub (May 11, 2023):

Moving that check would solve my problems, at least.

It seems like it ought to be possible to use awk to do this. I think even the busybox awk should be capable. And awk is already on the requirements list.

@drboone commented on GitHub (May 11, 2023): Moving that check would solve my problems, at least. It seems like it ought to be possible to use awk to do this. I think even the busybox awk should be capable. And awk is already on the requirements list.

adam commented

2025-12-29 01:27:45 +01:00

@dbrooke commented on GitHub (Jun 17, 2023):

I recently upgraded a SmartOS (Illumos derived) system and hit this issue.

For Linux and SmartOS (the only platforms I have readily available) the following seems equivalent so I thought I'd mention it even though I appreciate that it may not meet your portability requirements to other platforms and I've not tested it within dehydrated.

od -t x1 -An | tr -d " \n"

@dbrooke commented on GitHub (Jun 17, 2023): I recently upgraded a SmartOS (Illumos derived) system and hit this issue. For Linux and SmartOS (the only platforms I have readily available) the following seems equivalent so I thought I'd mention it even though I appreciate that it may not meet your portability requirements to other platforms and I've not tested it within dehydrated. od -t x1 -An | tr -d " \n"

adam commented

2025-12-29 01:27:46 +01:00

@bahamat commented on GitHub (Aug 6, 2024):

@lukas2511 So, I've been looking at this today, and I think od is probably a better solution all around. od is in coreutils, so it's going to be an exceedingly rare exception for a Linux system to not have it. On Debian/Ubuntu, hexdump is in the bsdmainutils or bsdextrautils package, not util-linux like it is on other distros. FreeBSD also does not have hexdump (the command is named hd instead).

Using od -t xC -An | tr -d '[:space:]' produces identical output to hexdump -v -e '/1 "%02x"'.

In addition to od being included in coreutils on Linux, od is also part of the base OS on FreeBSD, macOS, NetBSD, OpenBSD, and illumos, and has a consistent POSIX usage interface across each.

I also have prototyped testing all binary values from 00 to FF using both od and hexdump with the following script:

#!/bin/sh

a=( {0..3}{0..7}{0..7} )

printf 'hexdump control: '
for i in "${a[@]}" ; do
  printf "\\$i" | hexdump -v -e '/1 "%02x"'
done | sha1sum

printf 'od comparison:   '
for i in "${a[@]}" ; do
  printf "\\$i" | od -t xC -An | tr -d '[:space:]'
done | sha1sum

This script produces the following output:

$ ./compare.sh 
hexdump control: 330c1810efa17b806411ae71cfc79211e4b4aa01  -
od comparison:   330c1810efa17b806411ae71cfc79211e4b4aa01  -

So we have provably identical output to the existing implementation, and od is will be more widely and consistently available. Given this, I'll open a PR to switch from hexdump to od.

Let me know if you have any additional thoughts on this.

@bahamat commented on GitHub (Aug 6, 2024): @lukas2511 So, I've been looking at this today, and I think `od` is probably a better solution all around. `od` is in `coreutils`, so it's going to be an exceedingly rare exception for a Linux system to not have it. On Debian/Ubuntu, hexdump is in the bsdmainutils or bsdextrautils package, not util-linux like it is on other distros. FreeBSD also does not have `hexdump` (the command is named `hd` instead). Using `od -t xC -An | tr -d '[:space:]'` produces identical output to `hexdump -v -e '/1 "%02x"'`. In addition to `od` being included in `coreutils` on Linux, `od` is also part of the base OS on FreeBSD, macOS, NetBSD, OpenBSD, and illumos, and has a consistent POSIX usage interface across each. I also have prototyped testing all binary values from `00` to `FF` using both `od` and `hexdump` with the following script: ```sh #!/bin/sh a=( {0..3}{0..7}{0..7} ) printf 'hexdump control: ' for i in "${a[@]}" ; do printf "\\$i" | hexdump -v -e '/1 "%02x"' done | sha1sum printf 'od comparison: ' for i in "${a[@]}" ; do printf "\\$i" | od -t xC -An | tr -d '[:space:]' done | sha1sum ``` This script produces the following output: ```sh $ ./compare.sh hexdump control: 330c1810efa17b806411ae71cfc79211e4b4aa01 - od comparison: 330c1810efa17b806411ae71cfc79211e4b4aa01 - ``` So we have provably identical output to the existing implementation, and `od` is will be more widely and consistently available. Given this, I'll open a PR to switch from `hexdump` to `od`. Let me know if you have any additional thoughts on this.

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Reference: starred/dehydrated#601

hexdump is a linux only tool #601

`hexdump` is a linux only tool #601