ccache failed to create temp files in /var/cache/ccache/ , permission denied. On Gentoo Linux - linux

Question

System Info:
OS : Gentoo Linux x86_64
Kernel : Linux 5.4.38
CPU : Intel core i7-7820HQ
RAM : 16GiB
CC : GCC 9.3.0
This problem always happens when I install the emerge software.
My ccache directory is mounted on /dev/sda2, which is a primary partition in btrfs.
The corresponding directory permissions have been set.
/etc/fstab I posted below.
This is one of error messages:
==> COMPILING "OBJ/amd64-linux-cc/pic/fcons.o"
+ x86_64-pc-linux-gnu-gcc -fpic -march=native -O2 -pipe -finput-charset=ISO-8859-1 -fexec-charset=UTF-8 -DSCHILY_BUILD -IOBJ/amd64-linux-cc/pic -I../incs/amd64-linux-cc -I../include -Istdio -DUSE_SCANSTACK -DPORT_ONLY -D_GNU_SOURCE -c -o OBJ/amd64-linux-cc/pic/fcons.o stdio/fcons.c
ccache: error: Failed to create temporary file for /var/cache/ccache/7/d/f/cc59f6a892af180b36bf0d7b73f8c-148524.o.tmp.stdout: Permission denied
make[2]: *** [../RULES/r-gmake.obj:51: OBJ/amd64-linux-cc/pic/fcons.o] Error 1
make[2]: Leaving directory '/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/work/cdrtools-3.02/libschily'
make[1]: *** [../RULES/rules.mks:23: all] Error 2
make[1]: Leaving directory '/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/work/cdrtools-3.02/libschily'
make: *** [RULES/rules1.dir:25: all] Error 2
* ERROR: app-cdr/cdrtools-3.02_alpha09-r2::gentoo failed (compile phase):
* emake failed
*
* If you need support, post the output of `emerge --info '=app-cdr/cdrtools-3.02_alpha09-r2::gentoo'`,
* the complete build log and the output of `emerge -pqv '=app-cdr/cdrtools-3.02_alpha09-r2::gentoo'`.
* The complete build log is located at '/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/temp/build.log'.
* The ebuild environment file is located at '/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/temp/environment'.
* Working directory: '/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/work/cdrtools-3.02'
* S: '/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/work/cdrtools-3.02'
Failed to emerge app-cdr/cdrtools-3.02_alpha09-r2, Log file:
'/var/tmp/portage/app-cdr/cdrtools-3.02_alpha09-r2/temp/build.log'
ccache config & status:
(default) base_dir =
(environment) cache_dir = /var/cache/ccache
(/var/cache/ccache/ccache.conf) cache_dir_levels = 3
(/var/cache/ccache/ccache.conf) compiler = gcc
(/var/cache/ccache/ccache.conf) compiler_check = %compiler% -v
(/var/cache/ccache/ccache.conf) compression = true
(/var/cache/ccache/ccache.conf) compression_level = 1
(default) cpp_extension =
(default) debug = false
(default) depend_mode = false
(default) direct_mode = true
(default) disable = false
(default) extra_files_to_hash =
(default) hard_link = false
(default) hash_dir = true
(default) ignore_headers_in_manifest =
(default) keep_comments_cpp = false
(default) limit_multiple = 0.8
(default) log_file =
(default) max_files = 0
(/var/cache/ccache/ccache.conf) max_size = 100.0G
(/var/cache/ccache/ccache.conf) path = /usr/bin:/usr/local/bin
(default) pch_external_checksum = false
(default) prefix_command =
(default) prefix_command_cpp =
(default) read_only = false
(default) read_only_direct = false
(default) recache = false
(default) run_second_cpp = true
(default) sloppiness =
(default) stats = true
(default) temporary_dir =
(default) umask =
cache directory /var/cache/ccache
primary config /var/cache/ccache/ccache.conf
secondary config (readonly) /etc/ccache.conf
stats updated Sat May 23 16:40:07 2020
cache hit (direct) 4029
cache hit (preprocessed) 860
cache miss 19704
cache hit rate 19.88 %
called for link 3119
called for preprocessing 2708
multiple source files 2
compiler produced stdout 4
compiler produced empty output 30
compile failed 1624
preprocessor error 247
couldn't find the compiler 2
bad compiler arguments 464
autoconf compile/link 5507
unsupported compiler option 835
unsupported code directive 4
could not write to output file 90
no input file 1576
cleanups performed 0
files in cache 52712
cache size 1.2 GB
max cache size 100.0 GB
some info of /var/cache/ccache:
drwxrwsr-x 1 root portage 66 May 23 16:40 0
drwxrwsr-x 1 root portage 66 May 23 16:38 1
drwxrwsr-x 1 root portage 66 May 23 16:39 2
drwxrwsr-x 1 root portage 66 May 23 16:38 3
drwxrwsr-x 1 root portage 66 May 23 16:38 4
drwxrwsr-x 1 root portage 66 May 23 16:38 5
drwxrwsr-x 1 root portage 66 May 23 16:38 6
drwxrwsr-x 1 root portage 66 May 23 16:38 7
drwxrwsr-x 1 root portage 66 May 23 16:38 8
drwxrwsr-x 1 root portage 66 May 23 16:38 9
drwxrwsr-x 1 root portage 66 May 23 16:38 a
drwxrwsr-x 1 root portage 66 May 23 16:38 b
drwxrwsr-x 1 root portage 66 May 23 16:38 c
-rwxrwxr-x 1 root portage 209 May 23 11:17 ccache.conf
drwxrwsr-x 1 root portage 66 May 23 16:38 d
drwxrwsr-x 1 root portage 66 May 23 16:40 e
drwxrwsr-x 1 root portage 66 May 23 16:38 f
drwxrwsr-x 1 portage portage 0 May 23 16:38 tmp
fstab :
UUID=EA7D-E1DB /boot vfat defaults,noatime,discard 0 2
UUID=4f174448-dcef-4e12-ae0a-f5c79cfe3da6 none swap sw,discard 0 0
UUID=1bb4ace3-1fba-4068-bea7-e7d307d56fa3 / btrfs noatime,discard 0 1
UUID=81210f26-8349-4aed-9ad4-55626fc10be9 /home btrfs noatime,discard 0 1
UUID=c8f65f22-8271-4457-a891-4e877fb2b98c /var/cache/ccache btrfs noatime,discard 0 1
make.conf :
COMMON_FLAGS="-march=native -O2 -pipe"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"
PORTDIR="/var/db/repos/gentoo"
DISTDIR="/var/cache/distfiles"
PKGDIR="/var/cache/binpkgs"
LC_MESSAGES=C
MAKEOPTS="-j2 -l2"
GENTOO_MIRRORS="https://mirrors.tuna.tsinghua.edu.cn/gentoo"
INPUT_DEVICES="libinput evdev vmmouse touchpad joystick synaptics"
VIDEO_CARDS="nvidia"
USE_PYTHON="3.7"
PYTHON_TARGETS="python3_7"
USE="static-libs systemd dbus policykit udisks acpi bluetooth X alsa qt5 gtk kde wayland pulseaudio mysql networkmanager thunderbolt zsh-completion apparmor -ssh"
CPU_FLAGS_X86="aes avx avx2 f16c fma3 mmx mmxext pclmul popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3"
PORTAGE_ELOG_CLASSES="log"
PORTAGE_ELOG_SYSTEM="save"
FEATURES="ccache nostrip"
CCACHE_DIR="/var/cache/ccache"