For example:
https://uberchromegw.corp.google.com/i/chromeos/builders/rambi-release/builds/961


02:29:23: INFO: RunCommand: /b/cbuild/internal_master/chromite/bin/cros_sdk 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpCh2CDx' -- /mnt/host/source/chromite/bin/cros_extract_deps '--format=deps' virtual/target-sdk chromeos-base/chromite --output-path /tmp/tmpFmtzuc in /b/cbuild/internal_master
02:29:38: INFO: RunCommand: /b/cbuild/internal_master/chromite/bin/cros_sdk 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpzMZ3GF' -- /mnt/host/source/chromite/bin/cros_extract_deps --board rambi '--format=deps' virtual/target-os virtual/target-os-dev virtual/target-os-test virtual/target-os-factory virtual/target-os-factory-shim chromeos-base/autotest-all --output-path /tmp/tmpkjGhJY in /b/cbuild/internal_master
02:30:30: INFO: Recording packages under test
02:30:30: INFO: RunCommand: /b/cbuild/internal_master/chromite/bin/cros_sdk '--chrome_root=/b/cbuild/internal_master/.cache/distfiles/target/chrome-src-internal' 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpxE4jq4' 'USE=-cros-debug chrome_internal afdo_use' 'FEATURES=separatedebug' 'CHROME_ORIGIN=LOCAL_SOURCE' -- ./build_packages '--board=rambi' '--accept_licenses=@CHROMEOS' --withdebugsymbols --skip_chroot_upgrade --nousepkg --reuse_pkgs_from_local_boards --noworkon virtual/target-os virtual/target-os-dev virtual/target-os-test virtual/target-os-factory virtual/target-os-factory-shim chromeos-base/autotest-all in /b/cbuild/internal_master
ERROR   cros_sdk:enter_chroot: Not mounting chrome source: could not find CHROME_ROOT/src dir.
ERROR   cros_sdk:enter_chroot: Full path we tried: /b/cbuild/internal_master/.cache/distfiles/target/chrome-src-internal/src
ERROR   cros_sdk:enter_chroot: Wed Jun 29 02:30:31 PDT 2016
ERROR   cros_sdk:enter_chroot:  PGID  PPID   PID     ELAPSED     TIME %CPU COMMAND
ERROR   cros_sdk:enter_chroot: Arguments of 10:  '--chroot' '/b/cbuild/internal_master/chroot' '--cache_dir' '/b/cbuild/internal_master/.cache' '--chrome_root' '/b/cbuild/internal_master/.cache/distfiles/target/chrome-src-internal' '--' 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpxE4jq4' 'USE=-cros-debug chrome_internal afdo_use' 'FEATURES=separatedebug' 'CHROME_ORIGIN=LOCAL_SOURCE' '--' './build_packages' '--board=rambi' '--accept_licenses=@CHROMEOS' '--withdebugsymbols' '--skip_chroot_upgrade' '--nousepkg' '--reuse_pkgs_from_local_boards' '--noworkon' 'virtual/target-os' 'virtual/target-os-dev' 'virtual/target-os-test' 'virtual/target-os-factory' 'virtual/target-os-factory-shim' 'chromeos-base/autotest-all'
ERROR   cros_sdk:enter_chroot: Backtrace:  (most recent call is last)
ERROR   cros_sdk:enter_chroot:  enter_chroot.sh:551:main(), called: setup_env  
ERROR   cros_sdk:enter_chroot:  enter_chroot.sh:548:setup_env(), called: die 'setup_env failed' 
ERROR   cros_sdk:enter_chroot: 
ERROR   cros_sdk:enter_chroot: Error was:
ERROR   cros_sdk:enter_chroot:   setup_env failed
02:30:32: ERROR: 
return code: 1; command: /b/cbuild/internal_master/chromite/bin/cros_sdk '--chrome_root=/b/cbuild/internal_master/.cache/distfiles/target/chrome-src-internal' 'PARALLEL_EMERGE_STATUS_FILE=/tmp/tmpxE4jq4' 'USE=-cros-debug chrome_internal afdo_use' 'FEATURES=separatedebug' 'CHROME_ORIGIN=LOCAL_SOURCE' -- ./build_packages '--board=rambi' '--accept_licenses=@CHROMEOS' --withdebugsymbols --skip_chroot_upgrade --nousepkg --reuse_pkgs_from_local_boards --noworkon virtual/target-os virtual/target-os-dev virtual/target-os-test virtual/target-os-factory virtual/target-os-factory-shim chromeos-base/autotest-all
cwd=/b/cbuild/internal_master, extra env={'PARALLEL_EMERGE_STATUS_FILE': '/tmp/tmpxE4jq4', 'USE': '-cros-debug chrome_internal afdo_use', 'FEATURES': 'separatedebug', 'CHROME_ORIGIN': 'LOCAL_SOURCE'}

@@@STEP_FAILURE@@@
02:30:32: ERROR: ./build_packages failed (code=1)
02:30:32: INFO: Running cidb query on pid 32331, repr(query) starts with <sqlalchemy.sql.expression.Update object at 0x7fdcf80a9c90>
02:30:36: INFO: cidb query succeeded after 1 retries
02:30:36: INFO: Running cidb query on pid 32331, repr(query) starts with <sqlalchemy.sql.expression.Insert object at 0x7fdcf3daffd0>