Hey Keegan,
Thank you for your help. I just updated to 2021.8 but apparently, the error persists because I don't have sufficient space on my computer 
I tried this command:
(qiime2-2021.8) Aline-MBP:Analysis_Silva_full_length vetalinesantana$ qiime feature-classifier classify-sklearn --i-classifier silva-138-99-nb-classifier.qza --i-reads rep-seqs.qza --o-classification taxonomy.qza
I got this error:
(1/2) Invalid value for '--i-classifier': There was not enough space left on'/tmp' to extract the artifact 'silva-138-99-nb-classifier.qza'. (Try
setting $TMPDIR to a directory with more space, or increasing the size of
'/tmp')
(2/2) Invalid value for '--i-reads': There was not enough space left on
'/tmp' to extract the artifact 'rep-seqs.qza'. (Try setting $TMPDIR to a
directory with more space, or increasing the size of '/tmp')
I tried to create a TMPDIR (No space left on device classifier TMPDIR - #3 by thermokarst) and I got this error:
(qiime2-2021.8) Aline-MBP:Analise_Silva_full_length vetalinesantana$ mkdir /data
mkdir: /data: Read-only file system
(qiime2-2021.8) Aline-MBP:Analise_Silva_full_length vetalinesantana$ export TMPDIR='/data'
(qiime2-2021.8) Aline-MBP:Analise_Silva_full_length vetalinesantana$ echo $TMPDIR
/data
(1/2) Invalid value for '--i-classifier': There was not enough space left on '/tmp' to extract the artifact 'silva-138-99-nb-classifier.qza'. (Try
setting $TMPDIR to a directory with more space, or increasing the size of '/tmp') (2/2) Invalid value for '--i-reads': There was not enough space left on '/tmp' to extract the artifact 'rep-seqs.qza'. (Try setting $TMPDIR to a directory with more space, or increasing the size of '/tmp')
Do you know the minimum space to be able to perform my analysis with SILVA full length classifier? These are my computer settings:
qiime2-2021.8) Aline-MBP:Analise_Silva_full_length vetalinesantana$ df -h
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk1s5s1 113Gi 14Gi 12Gi 56% 553788 1181264652 0% /
devfs 189Ki 189Ki 0Bi 100% 654 0 100% /dev
/dev/disk1s4 113Gi 3.0Gi 12Gi 21% 3 1181818437 0% /System/Volumes/VM
/dev/disk1s2 113Gi 520Mi 12Gi 5% 2534 1181815906 0% /System/Volumes/Preboot
/dev/disk1s6 113Gi 5.3Mi 12Gi 1% 18 1181818422 0% /System/Volumes/Update
/dev/disk1s1 113Gi 83Gi 12Gi 88% 691200 1181127240 0% /System/Volumes/Data
map auto_home 0Bi 0Bi 0Bi 100% 0 0 100% /System/Volumes/Data/home
/Users/vetalinesantana/Downloads/FannyWidget-v2.3.0/Fanny.app 113Gi 63Gi 30Gi 68% 718654 1181099786 0% /private/var/folders/rc/h6g74q8j7b52b1d7drc57lhw0000gn/T/AppTranslocation/A60CA238-FB61-4B8E-9BCD-5495387BAEE5
Thanks!!!